Math dictionary of geometry words [www.onlinebcs.com]

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Math Dictionary of Geometry words: A-B
Acute Angle: Any angle measuring less than 90 Degrees
Acute
Triangle:
A triangle with ALL three angles being acute angles
Adjacent: Next to. You can have two building adjacent to each other.
Adjacent
Angles:
Angles that are IMMEDIATELY next to each other.
Adjacent
Sides:
Sides that are IMMEDIATELT next to each other.
Align:
When you arrange items in a straight line. You can allign edges
or even center points of shapes.
Alternate
Angles:
Angles opposite each other created by drawing one line accross
two others.
Altitude of
Shape:
The Perpendicular distance from the vertex of the shape to It's
base line.

Angle:
The amount of rotation, in an anti clockwise direction, between
two lines intersecting. These are measured by degrees.
Angle
Bisector:
A line that divides an angle into two equal parts.
Angle of
Rotation:
The number of degrees an object is rotated around a fixed
point. Always measured in a clockwise direction.
Anti-
Clockwise:
The opposite direction to the way the hands on an analogue
clock go.
Apex:
The highest point on a two dimensional or three dimensional
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: Does not have sides exactly the same.

Attribute:
This is a characteristic. Attributes can be color, size, shape. We
usually sort according to attributes.
Axis: These can be real or imaginary reference lines.
Axis of
Symmetry:
This is the line that diviedes symmetrical objects in half.
Base:
This can be the bottom line of a two dimensional shape or the
bottom face of a three dimensional face.
Bi-:
This is a prefix meaning 2 or twice of something. An example
is a bicycle - two wheels.
Bisect: To divide into two equal parts
Bisector:
A line, point or plane that divides something into two equal
parts
Boundary: A line around the outside edge - also known as perimeter.
Breadth:
Distance from one side of a shape to another - sometimes
referred to as width.

Math Dictionary of Geometry words: C-D
Calculate:
Perform mathematical operations
Calculator: A device used to perform mathematical operations
Capacity: The amount a container can hold
Carroll diagram: A sorting diagram named after Lewis Carroll
Cartesian plane:
Also called the coordinate plane. Contains two perpendicular
axes - X-Axis and Y-Axis. Points are plotted taking a
position from both the x and y axis. eg (3,10)
Chord: A line segment connecting two point on a circles perimiter.
Circle:
A plane shape drawn by a line whose points are equidistant
from the centre point of the circle.
Circumference: The distance around the circle. Calculated by: C = 2.Pi.r
Clockwise: The direction the hands on an anologue 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 through
parallel lines
Colinear: When objects are situated on the same line.
Colinear points: Three or more points that lie on the same line.
Compass
(construction):
An instrument used to create circles.
Complimentary
angle:
Two angles whose sum EQUALS 90 degrees
Concave: Curved inwards. The opposite of convex.
Concave
quadrilateral:
A quadrilateral with at least one reflex angle.
Concave
Polygon:
Any polygon with at least one reflex angle.

Concentric
Circle:
Circles different in size, but share a center point.
Cone:
A solid shape composed of an circular or eliptical 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
Quadrilaterals:
A quadrilateral where no angles are greater than 180 degrees
(reflex)
Coordinates:
Pairs of letters or numbers indicating a points position on the
cartesian/coordinate plane. They are always indicated with
the x-axis value first, then the y-axis. eg (4,7)
Coordinate plane: Same as 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:
Same as anti clockwise.
Cross Section: The face that results when a solid shape is cut.
Cube:
A solid shape whose form is created by 6 congruent squares.
Also one of the 5 Platonic Solids.
Cubic: The term used when describing a unit of volume.
Cuboid:
A right prism created by six rectangular faces. If all faces are
square it is called a cube.
Curve: A line that is NOT straight.

Cyclic
Quadrilaterals:
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 (angle): The unit which angles are measured by.
Diagonal: A line joining two NON-adjacent vertices.
Diameter:
A line connecting two points of a circle, which also includes
the centre 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 a remainder.
Dodeca: Prefix for 12.
Dodecagon: A polygon with 12 straight edges.
Dodechedron: A Polyhedron with 12 faces.
Math Dictionary of Geometry Words: E-F
Edge: Where two surfaces intersect or join
Elipse: A 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’s sign
showing that two expressions have the same value.

Equiangular: A shape that has all angles equal.
Equilateral
Triangle:
A triangle whose sides are all the same length.
Euler's formula:
For any convex Polyhedrons surface Eurlers 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 is infinite.
Flat: Having no depth.
Flip:
To 'turn over'. It is the term to describe a geometric
transformation.
Formula:
A rule, usually containing symbols (as it is true for all cases)
and describes the relationship between quantities

Math Dictionary of Geometry Definitions: G-H
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 relationships in space.
Graph: A drawing or diagram used to represent data.
Graph Paper:
Paper pre-printed with a specific scaled grid for ease of graph
drawing.
Half:
One of two equal parts. When an object is cut in two equal parts,
each porting is one half.
Height:
The perpendicular distance from the top of an object to the
bottom/base.
Hemisphere: A solid shape that is one half a sphere.
Hepta: Prefix meaning 7
Heptagon: A Polygon with seven sides.
Heptahedron: A Polyhedron with seven faces.
Hexa: Prefix meaning 6

Hexagon: A polygon with six sides.
Hexahedron: A polyhedron with six faces.
Horizontal:
The opposite of vertical. In geometry - A line parallel to the x-
axis. In life - a line parallel to the horizon. In this image, the base
of the tent is Horizontal.
Hypotenuse: The longest side of a right-angled triangle.
Math Dictionary of Geometry Words: I-J
Icosa: Prefix meaning 20
Icosagon: Polygon with 20 sides.
Icosahedrons: Polyhedron with 20 faces. One of the 5 platonic solids.
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:
An angle within a polygon. Angles within two lines, when
they are 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:
A shape which does not have all sides equal and all angles
equal.
Isometric: To have equal dimensions or measurements.
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 equal.
J:
I have not come across any geometry words beginning with
the letter J
Math Dictionary of Geometry Words: K-L
Kite:
A plane shape with two sets of equal lines, and one set of equal
angles.

>
Length: Distance from one end to another.
Line:
An infinite set of points going in opposite directions with an
angle of 180 degrees.
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.
Geometry Words starting with M-N
Maximum: Greatest value or amount. Highest point.
Measure:
Use of standard units to measures 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.
Numeral: Symbol used to represent a number.
Geometric Terms starting with O-P
Oblique: Lines at an angle to the x-axis.
Oblique Prism: A prism with bases not aligned directly above one another.
Obtuse angle: Any angle greater than 90 degrees and less than 180 degrees.
Obtuse Triangle: A triangle with one obtuse angle.
Octa: Prefix for 8
Octagon: An eight-sided polygon.

Octahedron: A polyhedron with 8 faces.
Order of
rotation:
How many times an outline matches its original during one
full rotation.
Ordered Pair:
Where information is given through a pair of numbers and the
order is critical. Ordered pairs are used in coordinate
geometry to indicate a points position. (1,3) is not the same as
(3,1)
Origin:
The point of intersection of the X-axis and 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: A 5-sided polygon.

Pentahedron: A Polyhedron with 5 faces.
Perimeter: The outline of a two-dimensional shape.
Perpendicular:
Two lines that meet at 90 degrees are said to be
perpendicular.
Perpendicular
Bisector:
A line that meets a line segment at 90 degrees AND bisects it.
Pi: The ratio of a circles circumpherence to its diameter.
Plane Shape: A flat shape with only two dimensions.
Platonic Solid:
Five Regular Polyhedral made only with either equilateral
triangles, squares or pentagons.
Poly: Prefix for MANY
Polygon: A plane shape with three or more straight sides.

Polyhedron: Three dimensional objects made with plane shapes.
Position:
Where something is when compared to an object or its
surroundings.
Prism:
Right Prism: A three-dimensional shape made of two
identical plane shapes, and all other faces are rectangles;
Oblique Prism: Made of two identical plane shapes, and all
other faces are parallelograms.
Protractor:
An instrument used in geometric construction to measure
degrees of angles.
Pyramid:
A three-dimensional shape with a polygon as its base and all
other faces congruent triangles that meet at the top (its vertex)
Pythagoras:
A Greek mathematician who lived circa 500BC. Famous for
his theorem on 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.
A Glossary of Geometry Words starting with Q-R
Quadrangle: A polygon with four angles and four sides.

Quadrant (circle): A quarter of a circle or a circles circumpherence.
Quadrant (Cartesian
Plane):
Any quarter section of the plane made by the
intersection of the X and Y-Axes
Quadrilateral: A polygon with four sides.
Quarter: One of four equal parts.
Radius: Distance from center to circumpherence of a circle.
Ratio: A comparative value of two or more amounts.
Ray: A line with a start points but no end point.
Rectangle:
A quadrilateral with four right angles and two pairs of
parallel lines.
Rectangular prism:
A polyhedron - a prism with two identical rectangles -
also known as a cuboid.

Reflection: A mirror images.
Reflex angle: Any angle between 180 degrees and 360 degrees.
Revolution: One complete turn through 360 degrees.
Rhombus:
A parallelogram with four equal sides and opposite
angles of equal size.
Right Angle: An angle measuring 90 degrees.
Rotation: To turn an object.
Rotational Symmetry:
If, when an object is rotated, it has the same outline as
its original shape.
Geometry Basics - Words starting with S-T
Scale: To enlarge or reduce.
Scalene Triangle: A triangle where all three sides are different in length

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
Semicircle: Half a circle.
Septa: Prefix for 7.
Septagon: A seven-sided 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 problem.

Sphere: A three dimensional solid that is perfectly round - a ball.
Square: A quadrilateral with four equal sides, and four right angles.
Straight Angle: Any angle that equals 180 degrees.
Straight Line: The shortest distance between two points.
Supplementary
angle:
Two angles whose sum is 180 degrees.
Surface:
A set of points that define a space. A surface can be flat or
curved.
Surface area: The total area of the surface of three-dimensional object.
Symmetry:
An object has symmetry when one half is a mirror image of
the other.

Tangent: A straight line that touches a circle at only one point.
Tangram: A square cut into seven pieces.
Tessellation: Patterns created from shapes that fit together with no gaps.
Tetrahedron:
A polyhedron with four triangular faces. It is one of the 5
platonic solids.
Three-
Dimensional:
Has three dimensions - length, breadth and height.
Transformation:
A change in position or size. Can be created by, flipping,
rotating, translating or enlarging.
Translation: Move an object in any direction without rotating it.
Trapezium: Quadrilateral with no parallel sides
Tri: Prefix for 3.

Triangle: Three-sided polygon.
Triangular prism:
A prism whose base are two identical triangles and all
other faces are rectangles.
Turn: Rotate around a fixed point.
Turning symmetry: Rotating an object about a point.
Two-Dimensional: Having only two dimensions - length and breadth.
Find your Geometry Definition - For any word starting with U-V
Unequal: Not equal.
Uniform cross
section:
When the cross section of a solid results in the same size at its
base.
Vertex: The point where sides or surfaces meet to make a corner.
Vertical:
At right angles to the horizon, or the x-axis on the Cartesian
plane. In the image, the telephone poles are vertical.

Vertically
Opposite:
Directly opposite.
Volume:
The capacity (measured in cubic units) of a three-dimensional
object.
Find any Geometry Word starting with W-X-Y-Z
Width:
Also known as Breadth. The distance from one side to another of
a shape or object.
X-Axis: The horizontal axis of the Cartesian Plane
X-
coordinate:
The position of a point in relation to the X-Axis. It is the first
element of the ordered pair of the point.
Y-Axis: The vertical axis of the Cartesian Plane
Y-
coordinate:
The position of a point in relation to the Y-Axis. It is the second
element of the ordered pair of the point.

Math dictionary of geometry words [www.onlinebcs.com]

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Math dictionary of geometry words [www.onlinebcs.com]