NAME______________________________________DATE____________
GEOMETRY TERMS
Define each of the following terms and draw a picture example of each.
Definition
Picture
1. diameter – a line segment that passes through the
center of a circle and has endpoints on
the circle, or the length of that segment
_______________________________________________________
2. radius - a line segment with one endpoint at the
center of a circle and the other endpoint
________on the circle, or the length of that segment_________________
3. chord – a line segment with endpoints on
___________a circle___________________________________________
4. segment – a part of a line with two endpoints
___________________________________________________________
5. ray – a part of a line with exactly one endpoint
__________________________________________________________
6. parallel lines – two lines that lie in the same
plane and do not intersect
__________________________________________________________
7. perpendicular lines – lines, segments, or rays
that intersect to form right angles
(intersect – have one endpoint in common)_________________________
8. intersecting lines – lines that cross at exactly
one point.
9. protractor – a tool for measuring angles
_____________________________________________________________
10.degree – a unit used to measure angles

___________________________________________________________
11.angle –formed by two rays with a common
endpoint
___________________________________________________________
12.vertex – the common endpoint of angles and
polygons
___________________________________________________________
13.acute angle – an angle that is less than 90 degrees
14.right angle – an angle that measures exactly 90
15.obtuse angle – an angle that is greater than 90
degrees, but less than 180.
___________________________________________________________
16.straight angle – measures exactly 180 degrees
___________________________________________________________
17. adjacent angles – share a vertex and a side but no
points in their interior
___________________________________________________________
18.vertical angles – a pair of opposite angles formed
by intersecting angles.
19.complementary angles – two angles whose
measures add up to 90 degrees
___________________________________________________________
20.supplementary angles –two angles whose measures
add up to 180 degrees
___________________________________________________________
21.leg – in a right triangle, the sides that include the
right angle; in an isosceles triangle, the pair
of congruent sides.
22. hypotenuse – in a right triangle, the side opposite
the right angle
23.cross sections - a plane figure obtained by
Slicing a solid with a plane
=
___________________________________________________________
24.corresponding angles –a pair of angles formed by
a transversal and two lines
___________________________________________________________
25.acute triangle – a triangle with three acute angles
___________________________________________________________
26.obtuse triangle – a triangle with one obtuse angle
___________________________________________________________
27.right triangle – a triangle with one right angle
28.equilateral triangle – a triangle with three
congruent sides
___________________________________________________________
29.isosceles triangle – a triangle with two congruent
sides
___________________________________________________________
30.scalene triangle – a triangle with no congruent
sides
___________________________________________________________
31.polygon – a closed plane figure with at least
3 straight sides
____________________________________________________________
32.regular polygon – a polygon in which all
sides and angles are congruent.
____________________________________________________________
33. quadrilateral – a polygon with 4 sides
___________________________________________________________
34.parallelogram – a quadrilateral with both pairs
of opposite sides parallel
___________________________________________________________
35.rectangle – a parallelogram with four right angles
_____________________________________________________________
36.rhombus – a parallelogram with four congruent
sides
___________________________________________________________
37.square – a parallelogram with four right angles
and four congruent sides
___________________________________________________________
38.trapezoid – a quadrilateral with exactly one pair
_________
of parallel sides___________________________________
39.pentagon – a polygon with 5 sides
_____________________________________________________________
40.hexagon – a polygon with 6 sides
41.octagon – a polygon with 8 sides
__________________________________________________________
42.decagon – a polygon with 10 sides.
43.congruent – figures with corresponding
angles and sides that have
________________ equal measures _______________________________
44.similar – figures that have equal angles
________________and proportionate sides__________________________
45.corresponding sides – matching sides of two or
more polygons
46. circumference – the distance around a circle
C = d Π or C = 2r Π
_____________________________________________________________
47.irregular polygon - a polygon with sides not
equal and/or angles not equal
________________________
48.pi – the relationship of the circle’s circumference
Π = 3.14 or 22/7
to its diameter
49.arc – a part of a circle named by its endpoints
50. circle – the set of all points in a plane that are
the same distance from a given point
called the center
51. sector – a region enclosed by two radii and the
arc joining their endpoints
52.area – the number of square units needed to
cover a given surface
53. surface area - the sum of the areas of the faces
or surfaces of a 3 D figure
54. volume – the number of cubic units needed to
fill a given space
A=lxw
SA = 2lw + 2lh + 2hw
V = lwh
Please copy the following terms, definitions, and pictures on an empty space on any
of your pages. (Try your best with the pictures but don’t worry if it’s not perfect.)
They are not on the original copy you were given.
55. net – an arrangement of 2 dimensional figures that can be folded to form
a polyhedron
56. polyhedron – a 3D figure in which all the surfaces or faces are polygons.
57. solid figure – 3 D figure
58. prism – a polyhedron that has two congruent polygon-shaped bases and
other faces that are all parallelograms.