Geometry for Elementary School/Glossary

Below is a glossary of words used in this book.

A

 * Acute angle: An angle that is less than 90 degrees
 * Adjacent angle:	When two angles share the same vertice, and one same but opposite arm
 * Adjacent angles on a straight line:	When angles add up to 180 degrees and are adjacent
 * Altitude:	The line drew from the base to the tip of the triangle
 * Angle sum of triangles: The angle sum of triangles is 180 degrees
 * Angles at a point:	When angles add up to 360 degrees and are adjacent
 * Arc:	A part of a circumference
 * Area:	How big a plane shape is
 * Arms:	One of the two rays in an angle
 * Axiom:	Similar to a theorem, except it is thought up rather than proved

B

 * Base:	Any side of the triangle

C

 * Centre:	The middle of a shape, especially a circle
 * Chord:	A line that goes from one point of the circumference to another with touching the centre
 * Circle:	A shape with infinite loci that are the same distance from the circle
 * Colinear:	When two points are on the same line
 * Complementary angles:	Angles that add up to 90 degrees
 * Cone:	A shape with a circle as a base and a pointy top
 * Coplanar:	When two points or lines are on the same plane.
 * Cross-section:	The shape formed after cutting a solid
 * Cube:	A hexahedron with all edges equal
 * Cuboid:	A rectangular prism
 * Curved surface:	A surface that is not smooth
 * Cylinder:	A shape with parallel, congruent circles as bases

D

 * Decagon:	A polygon with ten sides
 * Decahedron:	A polyhedron with ten sides
 * Degree:	The unit used for measuring angles
 * Diameter:	The line that goes from one point of the circumference, through the centre and to another side of the circumference
 * Dimension:    The kind of space that a shape is in. If a shape has 2-dimensions, it has width and length; if it has three, it has width, height and length.
 * Dissecting:	A method of finding the area of a polygon
 * Dodecagon:	A polygon with twelve sides
 * Dodecahedron:	A polyhedron with twelve sides

E

 * Edge:	The edge of a solid
 * Ellipse:	A shape that looks like an oval
 * Equiangular:	When a polygon's angles are identical
 * Equilateral:	When a polygon's sides are identical
 * Euler's formula:	Faces + Vertices - Edges = 2

F

 * Face:	A plane figure on a solid
 * Filling:	A method of finding the area of a polygon
 * Finite:	Not unlimited
 * Focus:	One of the two points in the middle of a ellipse

H

 * Height:	The third dimension of a solid or the altitude of a triangle
 * Heptagon:	A polygon with seven sides
 * Heptahedron:	A polyhedron with seven sides
 * Hexagon:	A polygon with six sides
 * Hexahedron:	A polyhedron with six sides

I

 * Intersect:	When two or more lines, planes, etc., cross each other
 * Irregular:	Not regular
 * Isosceles trapezium:	A trapezium with two sides equal
 * Isosceles triangle:	A triangle with two sides identical

K

 * Kite:	A quadrilateral where two pairs of adjacent sides are equal and one pair of opposite angles is equal

L

 * Line:	A series of colinear points which extends in both directions forever; has no width
 * Line of intersection:	The line formed when two planes intersect
 * Line segment:	A line with a fixed length, with two endpoints

N

 * Nonagon:	A polygon with nine sides
 * Nonahedron:	A polyhedron with nine sides

O

 * Obtuse angle:	An angle between 90 and 180 degrees
 * Octagon:	A polygon with eight sides
 * Octahedron:	A polyhedron with eight sides

P

 * Parallel line:	Two lines that never intersect
 * Parallelogarm:	A quadrilateral where opposite sides and angles are equal
 * Pentagon:	A polygon with five sides
 * Pentahedron:	A polyhedron with five sides
 * Perimeter:	The sum of a plane shape's sidse
 * Perpendicular line:	When two lines intersect to create right angles
 * Pi:	The ratio of the diameter and the circumference
 * Plane:	A plane that extends in all directions forever; has no thickness
 * Point:	A dot that is so small that its height and width are actually zero
 * Point of intersection:	The point formed when two lines intersect
 * Polygon:	A shape that has straight sides
 * Postulate:	See Axiom
 * Prism:	A shape with parallel, congruent bases
 * Protractor:	A tool for measuring angles
 * Pyramid:	A shape with a base and a pointy top

Q

 * Quadrilateral:	A polygon with four sides

R

 * Radius:	The line that goes from the centre to one point of the circumference
 * Ray:	A line that only extends in one direction forever
 * Rectangle:	A quadrilateral opposite sides are equal and all angles are 90 degrees
 * Reflex angle:	An angle between 180 and 360 degrees
 * Regular:	When a polygon is both equilateral and equiangular, or when a solid satisfies all the criteria for regular polyhedra
 * Rhombus:	A quadrilateral where all sides are equal and opposite angles are equal
 * Right angle:	An angle of 90 degrees
 * Right-angled trapezium:	A trapezium with a right angle
 * Round angle:	An angle of 360 degrees

S

 * Scalene trapezium:	A trapezium with neither a right angle nor equal sides
 * Semicircle:	Half a circle
 * Septagon:	See Heptagon
 * Septahedron:	See Heptahedron
 * Sphere:	A ball
 * Splitting:	See Dissecting
 * Square:	A regular quadrilateral where all sides are equal and all angles are equal
 * Straight angle:	An angle of 180 degrees
 * Supplementary angles:	Angles that add up to 180 degrees

T

 * Tetrahedron:	A polyhedron with four sides
 * Total surface area:	The total area of all faces of a solid
 * Trapezium:	A quadrilateral where there is one pair of parallel sides
 * Trapezoid:	See Trapezium
 * Triangle:	A polygon with three sides

U

 * Undecagon:	A polygon with eleven sides
 * Undecahedron:	A polyhedron with eleven sides
 * Uniform cross-sections:	The identical shapes formed after cutting the solid in the same direction; only on prisms and cylinders

V

 * Vertex:	A corner in things such as angles, plane figures and solids
 * Vertically opposite angles:	When angles share the same vertex and their opposite arms are on the same straight line; are always the same size.
 * Volume:	How big a solid is