GEOMETRY VOCABULARY
Name:________________________
Date: _________ Block:__________
1.
POINT: a mathematical figure pictured by a dot and named by a letter.
2.
LINE: a line segment extended without end in both directions.
3.
LINE SEGMENT: a part of a line consisting of two endpoints and all the
points between them.
4.
RAY: a line segment extended without end in one direction only.
5.
COLLINEAR POINTS: points that lie on the same line.
6.
ENDPOINT: a boundary point of a line segment or ray.
7.
PLANE: a set of points on a flat surface that extends without end.
8.
COPLANAR: points or lines in the same plane.
9.
COMPASS: a drawing instrument used to draw arcs and circles.
10.
CIRCLE: a plane figure with all points the same distance from a given point
called the center.
11.
CHORD: a segment with both endpoints on the circle.
12.
DIAMETER: in a circle, a segment that passes through the center and that has
both endpoints on the circle.
13.
ARC: part of a circle.
14.
SEMI-CIRCLE: an arc that joins the endpoints of a diameter.
15.
RADIUS: in a circle, a segment that has one endpoint on the circle and the
other endpoint on the center of the circle.
16.
TANGENT: a line that intersects a circle in exactly one point.
17.
CIRCUMFERENCE: the distance around a circle.
18.
PI: the ratio of a circle’s circumference divided by its diameter.
19.
ANGLE: the figure formed by two rays sharing a common endpoint called a
vertex.
20.
SIDE:
a.) one of the rays of an angle
b.) a line segment whose endpoints are adjacent vertices of a polygon.
21.
VERTEX:
a.) the common endpoint of two rays that form an angle.
b.) the point of intersection of two sides of a polygon.
c.) the point of intersection of the edges of a polyhedron.
22.
ADJACENT ANGLES: angles that have a common vertex and share a
common side between them.
1
4
2
3
23.
VERTICAL ANGLES: angles formed by intersecting lines and sharing only a
vertex.
24.
PROTRACTOR: a device for measuring angles in units called degrees.
25.
BISECT: to divide into two congruent parts.
26.
ACUTE ANGLES: an angle whose measure is between 0  and 90  .
27.
RIGHT ANGLES: an angle whose measure is 90 
28.
OBTUSE ANGLES: an angle whose measure is between 90  and 180  .
29.
STRAIGHT ANGLES: an angle whose measure is 180  .
30.
PERPENDICULAR LINES: lines that intersect to form right angles.
31.
EQUAL ANGLES: angles with the same measure.
32.
COMPLEMENTARY ANGLES: angles whose measures add up to 90  .
33.
SUPPLEMENTARY ANGLES: angles whose measures add up to 180  .
34.
CENTRAL ANGLE: an angle with its vertex at the center of the circle.
35.
POLYGON: a closed plane figure made by line segments.
36.
REGULAR POLYGON: a polygon with all sides congruent and all angles
congruent.
37.
TRIANGLE: a polygon with 3 sides.
38.
ACUTE TRIANGLE: a triangle with three acute angles.
39.
OBTUSE TRIANGLE: a triangle with an obtuse angle.
40.
RIGHT TRIANGLE: a triangle with a right angle.
41.
SCALENE TRIANGLE: a triangle with no congruent sides.
42.
ISOSCELES TRIANGLE: a triangle with at least two congruent sides.
43.
EQUILATERAL TRIANGLE: a triangle with all three sides congruent.
44.
QUADRILATERAL: a polygon with 4 sides.
45.
TRAPEZOID: a quadrilateral with exactly one pair of parallel sides.
46.
ISOSCELES TRAPEZIOD: a trapezoid with non parallel sides congruent.
47.
PARALLELOGRAM: a quadrilateral with opposite sides parallel and
congruent.
48.
RHOMBUS: a parallelogram with all sides congruent.
49.
RECTANGLE: a parallelogram with four right angles.
50.
SQUARE: a rectangle with congruent sides or a rhombus with four right
angles.
51.
PENTAGON: a polygon with 5 sides.
52.
HEXAGON: a polygon with 6 sides.
53.
HEPTAGON: a polygon with 7 sides.
54.
OCTAGON: a polygon with 8 sides.
55.
NONAGON: a polygon with 9 sides.
56.
DECAGON: a polygon with 10 sides.
57.
CONGRUENT POLYGONS: polygons that are the same shape and size.
58.
SIMILAR POLYGONS: polygons that are the same shape and proportional in
size.
59.
DIAGONAL: a segment with two non-adjacent vertices of a polygon as its
endpoints.
60.
SYMMETRIC FIGURE: a plane figure that can be folded into two congruent
parts. The fold is the line of symmetry.
61.
PARALLEL LINES: coplanar lines which never intersect.
62.
TRANSVERSAL: a line which intersects two or more lines in the same plane
(cuts the parallel lines)
63.
ALTERNATE INTERIOR ANGLES: angles between parallel lines and on
opposite sides of the transversal (look for the Z)
64.
CORRESPONDING ANGLES: angles having the same position on each of
the parallel lines (look for the F)

X
Q
1
Y
2
3
W
4
5
Z
6
7
8

65.
P
SKEW LINES: lines which are not coplanar - they do not intersect and are not
parallel.