Geometry Vocabulary
1. 1 dimensional figure - an object measured in 1 direction (length)
2. line segment - a part of a line with 2 endpoints
3. line - a straight path on a plane, that goes on and on in 2 directions
4. ray - a part of a line with 1 endpoint that goes on and on in 1 direction
5. parallel lines - 2 lines that are the same distance apart
6. intersecting lines - lines that cross and meet at exactly 1 point
7. perpendicular lines - lines that cross or meet to form right angles
8. right angle - measures exactly 90 degrees; a “perfect” corner
9. acute angle - smaller than a right angle (“a cute little angle”)
10. obtuse angle - larger or open wider than a right angle
11. 2 dimensional figure - an object measured by length and width
12. plane figure - a figure that lies on a plane; flat; 2D
13. circle - a curved plane figure with each point on the curved line being the same distance from its
center point
14. polygon - a closed plane (flat) figure with straight sides
15. vertex/vertices - the point where 2 line segments meet in 2D objects, or where 3 faces meet in
3D objects
16. triangle - a polygon with 3 sides, angles, angles and vertices
17. quadrilateral - any polygon with 4 sides and 4 angles; There are 6 types: square, rectangle,
parallelogram, rhombus, trapezoid, and a general quadrilateral
18. square - a polygon with 4 congruent sides and 4 right angles; its opposite sides are parallel and
congruent
19. rectangle - a polygon with 4 right angles, whose opposite sides are parallel and congruent
20. parallelogram - a polygon whose opposite sides are parallel and congruent (2 pairs of parallel
sides)
21. rhombus - a parallelogram whose 4 sides and opposite angles are congruent
22. trapezoid -a quadrilateral with only 1 pair of parallel sides
23. pentagon - a polygon with 5 sides, angles, and vertices
24. hexagon - a polygon with 6 sides, angles, and vertices
25. octagon - a polygon with 8 sides, angles and vertices
26. symmetry/lines of symmetry - a figure has a line of symmetry if it can be folded where the one
half is an exact fit on top of the other; a square has 4 lines of symmetry
27. congruent - same size and shape
28. transformation - the movement of any shape in geometry; 3 types: reflection, translation,
rotation
29. reflection - when 1 shape makes the mirror image of another shape; flip
30. translation - when 1 shape slides into another position; slide
31. rotation - when 1 shape turns around a point; turn
32. 3 dimensional figure - measured in 3 directions: length, width, and height
33. sphere - a 3D object with 1 curved surface
34. face - the flat surfaces that makes up a 3D figure
35. edge - the line segment where 2 faces meet
36. cube - a 3D object with 6 congruent square faces
37. rectangular prism - a 3D object with 6 rectangular faces
38. triangular prism - a 3D object with 2 triangular and 3 rect. faces
39. pyramid - ”spear-a-mid” 3 types: square, rectangular, triangular.
40. cylinder - has 2 flat faces and 1 curved surface; examples: tissue rolls, cans
41. cone - has 1 flat face and 1 curved surface; examples: party hats, ice cream cones