Geometry Dictionary - s3-us-west-2.amazonaws.com

GEOMETRYDICTIONARY

Having a resource of all the correctterminology for Kindergarten toSixth Grade Geometry, makes

learning the subject much easier.

Fully Illustrated

Open InvitationBring a coffee & pastry and join us in

K6Math Caféfor all Kindergarten Sixth Grade Math talk!

Bring your success.Bring your frustrations.Bring your questions.Post your kiddos Math Art on the wall.Come on over to give help and receive it!

Favebook.com/groups/K6MathCafe

https://www.facebook.com/groups/k6mathcafe

https://www.facebook.com/groups/k6mathcafe

By Niamh Juhl www.K6Math.com

Acute Angle:

Any angle measuring greater than 0° and less

than 90°

Acute Triangle:

A triangle where ALL THREE angles are acute

angles. See Acute Angle

Adjacent Angles:

Angles that are IMMEDIATELY next to each

other.

Adjacent Sides:

Sides of a shape that are IMMEDIATELY next to

each other.

Align:

When you arrange items in a straight line. You

can align edges or even center points of shapes.


Alternate:

Angles opposite each other when created by

drawing a transversal line. See Transversal Line

Altitude:

The perpendicular distance from the highest

vertex of a shape to the shapes base line.

Angle:

The amount of rotation, in an anticlockwise

direction, between two intersecting lines,

measure by degrees.

Angle Bisector:

The name given to a line, line segment or ray;

that divides an angle into two equal parts.

Angle of Rotation:

The number of degrees an object is rotated

around a fixed point. This is always measured

in a clockwise direction.


Anti-Clockwise:

The opposite direction to the way the hands on

an analogue clock move.

Also known as counter clockwise.

Apex:

The highest point on a two-dimensional (2D) or

three-dimensional (3D) shape.

Arc:

A section of a curve, or part of a circle.

Area:

The amount of SURFACE a shape occupies –

measured in square units.

Asymmetry:

A shape that does not have sides exactly the

same.


Attribute:

This is a characteristic. Attributes can be color,

size, shape or any other distinguishing

characteristic. We usually sort according to

attribute.

Axis:

This can be a real or an imaginary reference

line.

Axis of Symmetry:

This is the line that divides symmetrical shapes

in half.

Base:

This can be the bottom line of a two

dimensional shape, or the bottom face of a

three dimensional figure.

Bi-:

This is a prefix meaning two or twice of

something. An example: Bicycle – two wheels.

Bisect:

To divide into two equal parts.


Bisector:

A line, point or plane that divides something

into two equal parts.

Boundry:

A line creating the outside edge of a shape. It is

also known as the perimeter.

Breadth:

The distance from one side of a shape to its

other side. Sometimes referred to as ‘width’.

Calculate:

To perform mathematical operations.

Calculator:

A device used to perform mathematical

operations.

Capacity:

The amount a container can hold. Usually

measured in cubic units.


Carroll Diagram:

A sorting diagram named after Lewis Carroll.

Cartesian Plane:

Also called the coordinate plane. Contains two

perpendicular axis – X-Axis and Y-Axis. Points are

plotted taking a position from both the X and Y

axis. The X-Axis is always listed first. e.g. (3,10)

Chord:

A line segment connecting two points on a circles

perimeter.

Circle:

A plane shape drawn by a line whose points are

equidistant from any given point. A circle is a

closed curve.

Circumference:

The distance around (the boundary or perimeter) a

circle. Calculated by equation: P = 2πr

Clockwise:

The direction the hands on an analogue clock move.


Closed Curve:

Any curve where it joins itself at its starting point.

Cointerior Angles:

The inner angles on the SAME SIDE of a line drawn

across to parallel lines.

Colinear:

When objects are situated on the same line.

Colinear Points:

Three or more points that lie on the same line.

Compass:

An instrument used to create circles

Complimentary Angles:

Two angles whose SUM equals 90°


Concave:

Curved inwards. The opposite of convex.

Concave Quadrilateral:

A quadrilateral with at least one reflex angle.

Concave Polygon:

A polygon with at least one reflex angle.

Concentric Circles:

Circles different in size, but sharing a center point.

Cone:

A solid shape composed of a circular or elliptical

base, and a curved surface which tapers to a vertex.


Congruent Figures:

A congruent figure has all equal sides and all equal

angles.

Converging Lines:

Lines that all head in the direction of the same

point.

Convex:

Curved outwards – the opposite of concave.

Convex Quadrilateral:

A quadrilateral where no angles are greater than

180° (reflex)

Coordinates:

Pairs of letters or numbers indicating a points

position on the Cartesian/coordinate plane. These

are always indicated with the X-Axis value first

followed by the Y-Axis.


Coordinate Plane:

See Cartesian Plane.

Coplanar:

Geometric objects that exist on the same plane.

Corner:

The points where surfaces/vertices meet.

Corresponding Angles:

Angles that have the same position created by one

line intersecting two or more parallel lines.

Counter Clockwise:

See Anti Clockwise


Cross Section:

The face that results when a solid shape is cut.

Cube:

A solid form whose shape is created by six

congruent squares. A Cube is also a Platonic Solid.

Cubic:

The term used when describing a unit of volume.

Cuboid:

A right prism created by six regular faces. If all faces

are square it is said to be a cube.

Curve:

A line that is NOT straight.

Cyclic Quadrilateral:

A quadrilateral where a circle can be circumscribed

to contain ALL four vertices.


Cylinder:

A solid shape composed of two congruent circles

and one curved surface.

Deca-:

Prefix meaning 10.

Decagon:

A 10 sided polygon.

Decahedron:

A polyhedron with 10 faces.

Decrease:

To make smaller in size.

Deduct:

To subtract or take away.

Degree:

The unit which angles are measured by.

Diagonal:

A line joining two NON-adjacent vertices.


Diameter:

A line connecting two points on a circle which also

INCLUDES the central point of the circle.

Diamond:

A plane shape with 4 equal sides and NO right

angles. Also known as a Rhombus.

Distance:

The length between two points or objects.

Divisible:

Can be divided without remainders.

Dodeca:

Prefix for 12.

Dodecagon:

A polygon with 12 straight edges.


Edge:

Where two surfaces intersect, or join.

Ellipse:

An oval shaped plane shape, resembling a flattened

circle.

Endpoint:

The point denoting the end of a line segment.

Equation:

This is a mathematical statement containing an

equal sign showing that two expressions have the

same value.

Equiangular:

A shape that has all angles equal. All Regular

polygons are equiangular.


Equilateral:

A triangle whose sides are all the same length.

Euler’s Formula:

For any convex Polyhedrons surface, Euler’s Formula

states: V – E + F = 2 where V, E & F are vertices,

edges and faces.

Exterior Angles:

The angle formed on the outside of a Polygon, when

one side is extended.

Face:

The flat surface of a three-dimensional shape.

Finite:

Something that can be counted. It has a definite

beginning and end. The opposite of infinite.


Flat:

A shape that has no depth.

Flip:

To turn over. Flip is a term used to describe one

type of geometric transformation.

Formula:

A rule, usually containing symbols (as it is true for all

cases) and describes the relationship between

quantities.

Geometry:

One of the two earliest areas of math to be studied.

(The other was numbers). It studies the shapes,

solids, points, lines, rays and curves and their

relationship in space.

Graph:

A drawing or diagram used to represent data. There

are many types of graphs – this image shows a line

graph.


Half:

One of two equal parts. When an object is cut into

two equal parts, each portion is one half.

Graph Paper:

Paper pre-printed with a specific scaled grid for ease

of graph drawing.

Height:

The perpendicular distance from the top of an

object to the bottom/base.

Hemisphere:

A solid shape that is one half a sphere.

Heptagon:

A polygon with 7 sides.

Hepta - :

A prefix meaning 7.


Heptahedron:

A polyhedron with 7 faces.

Hexa-:

A prefix meaning 6.

Hexagon:

A polygon with six sides.

Hexahedron:

A polyhedron with six faces.

Horizontal:

The opposite of vertical. In geometry, a line is said

to be horizontal if it is parallel to the X-Axis. In this

image the base of the front triangular face of the

tent is horizontal.

Hypotenuse:

The longest side of a right angled triangle.


Icosa-:

Prefix meaning 20.

Icosagon:


Icosahedron:

A polyhedron made up of 20 faces.

Increase:

To make larger in size.

Infinite:

No definite end. The opposite of finite.

Infinity:

Unable to be counted – it has no end.

Interior Angles:

1: An angle within a polygon.

2: Angles within two lines, created when crossed by

a third (transversal) line.


Intersect:

Where lines cross one another. The point the lines

have in common is called the point of intersection.

Irregular Polygon:

A shape that does NOT have all sides equal or all

angles equal is said to be an Irregular Polygon.

Isometric:

To have equal dimensions or measurement.

Isometric Paper:

Paper created with dots (dot paper) or grids (grid

paper) to assist with isometric drawings.

Isosceles Triangle:

A triangle that has two sides equal in length. Its

base angles are also equal in measure.


Kite:

A plane shape – a quadrilateral, with two sets of

lines equal in length and one set of equal angles.

The lines joining opposite angles ALWAYS intersect

at 90°

Length:

Distance from one end to another.

Line:

An infinite set of points going in opposite directions,

with an angle of 180°

Line of symmetry:

An object or shape has a line of symmetry if it can

be divided into two equal and identical parts by that

line.

Line segment:

A section of a line with a beginning and end point.


Maximum:

Greatest value or amount. Highest point

Measure:

Use of standard units to measure size or quantity.

Measurement can be made of length, area, weight

(mass) volume, temperature and time.

Measurement:

The exact measure of an object or quantity.

Mono-:

Prefix for 1.

Nona-:

Prefix for 9.

Nonagon:

Polygon with 9 sides.

Numerals:

Symbols used to represent a number.


Oblique:

Lines at an angle to the X-Axis (Horizon)

Oblique Prism:

A prism with bases NOT aligned directly above each

other.

Obtuse Angle:

Any angle greater than 90° and less than 180°

Obtuse Triangle:

A triangle that contains one obtuse angle.

Octa-:

A prefix meaning 8.

Octagon:



Order of Rotation:

How many times an outline matches its original

during one full rotation.

Ordered Pair:

Ordered Pairs are used to indicate a points position

in geometry. (3,1) is NOT the same as (1,3). The

ORDER is essential.

Origin:

The point of intersection of the X-Axis and the Y-Axis

on the Cartesian plane.

Parallel lines:

Lines that will NEVER intersect.

Parallelogram

A quadrilateral with opposite sides equal in length,

and parallel.


Pattern

A repetition of objects.

Penta-:

Prefix for 5.

Pentagon:


Pentahedron:

A polyhedron with 5 sides.

Perimeter:

The outline of a two-dimensional shape.

Perpendicular:

Two lines that meet at 90° are said to be

perpendicular.


Perpendicular Bisector:

A line that intersects a line segment at 90° AND

bisects the line segment.

Pi:

The ratio of a circles circumference to its diameter.

The exact value of pi is yet to be identified. When

calculating with Pi, it is traditional to leave in symbol

form, use the value of 22/7 or use the value 3.14

Plane Shape:

A flat shape with only two dimensions, height and

width. It has no depth.

Platonic Solid:

A group of five Regular Polyhedra, made only with

equilateral triangles, squares or pentagons. The five

are: Cube, Tetrahedron, Octahedron, Icosahedron

and the Dodecahedron.

Polygon:

A plane shape with three or more straight lines.

Poly-:

Prefix for many.


Polyhedron:

A Three dimensional object made up of plane

shapes. Plural – Polyhedra.

Position:

Where something is when compared to another

object or its surroundings.

Prism:

1: Right Prism: A three dimensional shape made up

of two identical plane shapes, and all other faces are

rectangles.

2: Oblique Prism: See Oblique Prism.

Protractor:

An instrument used during geometric drawings to

measure the degrees of angles

Pyramid:

A three dimensional shape composed of a polygon

as its base, and all other faces congruent triangles

that meet at the top (a common vertex)


Pythagoras:

A Greek Mathematician who lived circa 500BC.

Famous for his theorems on the Right-Angled

Triangles.

Pythagorean Theorem:

In a right angled triangle, the square of the

hypotenuse is equal to the sum of the squares of the

other two sides.

Quadrangle:

A polygon with 4 sides and 4 angles.

Quadrant (Circle):

A quarter of a circle, or a quarter of a circles

circumference.

Quadrant (Cartesian Plane):

Any quarter of the plane made by the intersection

of the X and Y-Axes.


Quadrilateral:


Quarter:

One of four equal parts.

Radius:

Distance from the center to the circumference of a

circle.

Ratio:

A comparative value of two or more amounts.

Ray:

A line with a start point but no end point.

Rectangle:

A quadrilateral with 4 right angles and two sets of

parallel lines.


Rectangular Prism:

A polyhedron with two identical rectangular faces,

joined by all other faces which are congruent. Also

known as a cuboid.

Reflection:

A mirror image.

Reflex Angle:

Any angle measuring between 180° and 360°

Revolution:

One complete turn through 360°

Rhombus:

A quadrilateral with 4 equal sides, and where

opposite angles are equal. See Kite also.

Right Angle:

An angle measuring 90°


Rotation:

To turn an object.

Rotational Symmetry:

If, when an object is rotated, it has the SAME

OUTLINE as its original shape, it is said to have

Rotational Symmetry.

Scale:

To enlarge or reduce an object.

Scalene Triangle:

A triangle where all three sides have DIFFERENT

lengths.

Sector:

A section of a circle defined by two radii and an arc.

Segment:

A section of a circle defined by a chord and an arc.


Semi-Circle (Half Circle):

Half a circle.

Septa-:

Prefix for 7.

Septagon:


Shape:

A form or outline of an object.

Side:

The line or curve on the outside of a shape that joins

the shapes vertices.

Size:

How big or small something is.

Solid:

A three dimensional shape.


Solution:

Answer to a problems.

Sphere:

A 3-Dimensional solid where all surface points are

equidistant from a given point which is its center.

Square:

A quadrilateral with 4 sides equal in length, AND 4

right angles.

Straight Angle:

Any angle that equals 180°

Straight Line:

The shortest distance between two points.

Supplementary Angle:

Two angles whose sum is 180°


Surface:

A set of points that define a space. A surface can be

curved or flat.

Surface Area:

The total area of ALL surfaces of a three-dimensional

figure.

Symmetry:

An object has symmetry when one half is a mirror

image of the other half.

Tangent:

A straight line that touches a circle at ONLY one

point.

Tangram:

Traditionally - a square cut into seven pieces.

Many variations have been made using shapes other

than a square.


Tessellation:

Patterns created from shapes that fit together with

NO gaps.

Tetrahedron:

A polyhedron with four triangular faces. It is one of

the five Platonic Solids. See Platonic Solid also.

Three Dimensional (3D):

Has three dimensions – Length, Breadth (width) and

Height.

Transformation:

A change in position or size. It can be created by

flipping, rotating, translating or enlarging.

Trapezium:

A quadrilateral with NO parallel sides.

Translation:

To move an object in any direction without rotating

it.


Tri-:

Prefix meaning three.

Triangle:

A three sided polygon.

Triangular Prism:

A prism whose two bases are congruent triangles

and all other faces (3) are congruent rectangles.

Turn:

Rotate around a fixed point.

Turning Symmetry:

Rotating an object about a point.

Two Dimensional (2D):

Having only two dimensions; Length and Breadth.

Uniform Cross Section:

When a solid undergoes a cross section, and the

new resulting face is the same size as the solids

base, the cross section is said to be Uniform.


Vertex:

The point where sides or surfaces meet to create a

corner.

Vertical:

At right angles to the horizon, or the X-Axis on the

Cartesian Plane. In this image, the telephone poles

are vertical.

Vertically Opposite:

Directly opposite.

Volume:

The capacity of a three-dimensional object

measured in Cubic Units.


Width:

Also known as breadth. The distance from one side

of a shape to the other.

X-Axis:

The horizontal axis of the Cartesian Plane.

X-Coordinate:

The first element of an ordered pair. The position of

a point in relation to the X-Axis. In the example

(3,10) the value of the X-coordinate is 3.

Y-Axis:

The vertical axis of the Cartesian Plane.

Y-Coordinate:

The second element of an ordered pair. The

position of a point in relation to the Y-Axis. In the

example (3,10) the value of the Y-coordinate is 10.

Documents

Geometry Dictionary - s3-us-west-2.amazonaws.com