1. Mrs. Daniel’s Geometry Vocab List

2. Geometry
Definition: a branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space.

3. Reflectional Symmetry
Definition: All of the points on one side of the line exactly match with all of the points on the other side of the line.
Picture:

4. Rotational Symmetry
Definition: looks that same after you turn the image around a point by less than 180 degrees.
The number of times you can turn the image determines the type of rotational symmetry.
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5. Point Definition: Location only; it has no size.
How to Name: One capital letter.
Example: P
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6. Line
Definition: Straight continuous arrangement of infinitely many points.
How to Name: Two capital letters with a line with 2 arrows above it.
Example: 𝐶𝐷
Picture:

7. Plane
Definition: Flat surface that extends infinitely along its length and width.
How to Name: One capital script (cursive) letter.
Example: M
Picture:

8. Collinear
Definition: On the same line
Picture:

9. Coplanar
Definition: On the same plane
Picture:

10. Ray
Definition: A point on a line, and all the points that lie on one side of this point.
How to Name: Two capital letters and a line with one arrow above. The endpoint must be the first letter.
Example: 𝐹𝑅
Picture:

11. Line Segment Definition: Part of line. Does not extend indefinitely.
How to Name: Two capital letters and a line on top.
Example: 𝐴𝐵
Picture:

12. Midpoint
Definition: Point on a line segment that is the same distance from both end points.
Picture: (must be drawn with tic marks)

13. Congruent
Definition: Equal. The same length. The same size. The same measure.
Picture: Drawn with “tic” marks.

14. Bisects/Bisector Definition- Divides into two equal, congruent parts.
Line: divides into two congruent segments
Angle: divides into two congruent angles
Picture: (must be drawn with tic marks)

15. Angle Definition: Formed by two rays that share a common endpoint.
How to Name: One or three letters. Angle symbol (∠) in front.
Example: ∠B or ∠ABC
Picture:

16. Vertex Definition: Common endpoint of the two rays in an angle
Picture:

17. Perpendicular/Perpendicular Bisector
Definition: Lines that meet at a 90 degree angle.
Symbol: ⊥
For example: 𝐴𝐵 ⊥ 𝐶𝐷
Picture: (must be drawn with right angle mark)

18. Parallel Definition: Lines that never intersect (cross/touch).
Symbol: ∥
Example: 𝑆𝑇 ∥ 𝐶𝐺
Picture:

19. Complementary Angles Definition: 2 angles that add up to 90 degrees.
Picture:

20. Supplementary Angles Definition: 2 angles that add up to 180 degrees.
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21. Linear Pair of Angles
Definition: Two angles on one line. Sum to 180 degrees.
Picture:

22. Right Angle Definition: Angle measure of exactly 90 degrees.
Symbol: Drawn with a “box”
Picture:

23. Acute Angle Definition: Angle measure of less than 90 degrees.
Picture:

24. Obtuse Angle
Definition: Angle measure of more than 90 degrees, but less than 180.
Picture:

25. Polygon Definition: A closed figure.
How to Name: All capital letters. Use as many letter as sides to the polygon.
Some Examples:

26. Concave
Definition: Polygon dips inward (Some diagonals can be drawn outside the shape).
Picture:

27. Convex
Definition: Polygon only points outward. (No diagonals can be drawn outside the shape).
Picture:

28. Regular Polygon
Definition: A closed figure, with congruent sides and congruent angles.
Picture: All sides and angles marked congruent.

29. Perimeter Definition: Sum of the lengths of the sides.
Picture: Perimeter = 26cm

30. Area
Definition: The amount of space inside the boundary of a flat (2-dimensional) object such as a triangle or circle.
Picture:

31. Right Triangle Definition: A triangle with one 90 degree angle.
Picture: Marked with “box”

32. Acute Triangle Definition: A triangle with three acute angles.
Picture:

33. Obtuse Triangle
Definition: A triangle with one obtuse angle.
Picture:

34. Scalene Triangle Definition: Triangle with no congruent sides.
Picture: Each side is marked with a different number of hash marks.

35. Isosceles Triangle
Definition: Triangle with at least two congruent sides and two congruent angles. Picture: Marked with two congruent sides and two congruent angles.

36. Equilateral Triangle
Definition: Triangle with three congruent sides and angles.
Picture: Marked with three congruent sides and three congruent angles.

37. Quadrilateral
Definition: Any closed four-sided figure.
Some Examples:

38. Parallelogram
Definition: A quadrilateral with two pairs of parallel sides.
Picture: Marked parallel and congruent.

39. Rhombus Definition: Two pairs of parallel sides and 4 congruent sides.
Picture: Marked parallel and congruent.

40. Rectangle
Definition: Two pairs of parallel sides and 4 congruent angles
Picture: Marked parallel, congruent and 4 right angles.

41. Square Definition: 4 congruent sides and 4 congruent angles
Picture: Marked parallel, congruent and four right angles.

42. Circle
Definition: a set of all points in a plane at a given distance from a given point (center/origin).
Picture:

43. Radius/Diameter
Definition: The given distance from center/origin of the circle to the edge. Diameter is a chord that passes through the origin/center.
Picture:

44. Chord
Definition: A line segment whose endpoints lie on the circle. The diameter is the longest chord.
How to Name: Two capital letters and a line on top.
Example: 𝑃𝑄
Picture:

45. Tangent
Definition: A line that touches (intersects) the circle only once. The point the circle touches the circle is named the point of tangency.
Picture:

46. Semicircle
Definition: Half of a circle.
Picture:

47. Cylinder
Definition: a solid geometric figure that is composed of two parallel congruent circles (bases) and a rectangle as a lateral face.

48. Prism
Definition: solid geometric figure that has two parallel congruent bases that are connected by lateral faces that are parallelograms

49. Sphere
Definition: a round solid figure, or its surface, with every point on its surface equidistant from its center.

50. Cone
Definition: solid geometric figure that has a flat base (frequently, though not necessarily, a circle) and tapers to a point called the apex or vertex.

51. Pyramid
Definition: solid geometric figure formed by connecting a polygonal base with a point forming triangular lateral faces.