Geometry Vocabulary

Front 1

point

Back 1

think of it as a location; has no size; named with a single letter

Front 2

line

Back 2

think of it as a series of points that extends in opposite directions without end; named with two letters with a line above them

Front 3

space

Back 3

the set of all points

Front 4

plane

Back 4

think of it as a flat surface with no thickness; extends forever; named with three letters

Front 5

collinear points

Back 5

points that are on the same line

Front 6

coplanar

Back 6

lines or figures in the same plane

Front 7

postulate

Back 7

an accepted statement of fact

Front 8

axiom

Back 8

same as postulate

Front 9

segment

Back 9

part of a line consisting of two endpoints and all of the points between them; named using the two endpoints

Front 10

ray

Back 10

past of a line consisting of one endpoint and all of the points of the line on one side of the endpoint, named using the endpoint and one other point on the ray

Front 11

opposite rays

Back 11

two collinear rays with the same endpoint, they form a line

Front 12

parallel lines

Back 12

coplanar lines that never intersect; the symbol for parallel to is ||

Front 13

skew lines

Back 13

noncoplanar lines, NOT parallel and NEVER intersect

Front 14

parallel planes

Back 14

planes that do not intersect

Front 15

coordinate

Back 15

the distance and direction from zero

Front 16

congruent segments

Back 16

segments with the same lengths

Front 17

midpoint

Back 17

point that divides the segment into two congruent segments

Front 18

angle

Back 18

two rays with the same endpoint, named by three points on the angle with the vertex letter in the middle or just the vertex

Front 19

acute angle

Back 19

an angle whose measure is less than 90

Front 20

right angle

Back 20

an angle whose measure is 90

Front 21

obtuse angle

Back 21

an angle whose measure is between 90 and 180

Front 22

straight angle

Back 22

an angle whose measure is 180, a line

Front 23

congruent angles

Back 23

angles with the same measure

Front 24

construction

Back 24

using a straightedge and a compass to draw a geometric figure

Front 25

straightedge

Back 25

ruler with no markings on it

Front 26

compass

Back 26

tool used to draw circles

Front 27

perpendicular lines

Back 27

two lines that intersect to form right angles, symbol for perpendicular is *upside-down T*

Front 28

perpendicular bisector

Back 28

a line, segment or ray perpendicular to a segment at its midpoint

Front 29

angle bisector

Back 29

a ray that divides an angle into two congruent angles, endpoint is at vertex