Geometry

3. polyhedron with one face (known as the "base") a polygon and all the other faces triangles meeting at a common polygon vertex (known as the "apex")
5. a plane figure with four equal sides and four right (90°) angles.
6. the amount of space that a substance or object occupies, or that is enclosed within a container, especially when great.
8. a symmetrical three-dimensional shape, either solid or hollow, contained by six equal squares.
10. the extent or measurement of a surface
13. a polygon with three edges and three vertices.
15. a angle of 90°
16. the set of all points in a plane that are equidistant from a given point called the center of the circle
18. an angle less than 90°
19. a two-dimensional doubly ruled surface spanned by two linearly independent vectors

1. a round solid figure, or its surface, with every point on its surface equidistant from its center.
2. the enclosing boundary of a curved geometric figure, especially a circle.
4. an angle greater than 90°
7. a 0-dimensional mathematical object
8. the surface traced by a moving straight line (the generatrix) that always passes through a fixed point (the vertex)
9. a straight one-dimensional figure having no thickness and extending infinitely in both directions.
11. a quadrilateral whose four sides can be grouped into two pairs of equal-length sides that are adjacent to each other
12. a line section that can link two points.
14. a quadrilateral with one pair of opposite sides parallel.
17. any of a set of straight lines passing through one point