geometry

1. a flat surface on which a straight line joining any two points on it would wholly lie.
2. an angle whose sides lie in opposite directions from the vertex in the same straight line and which equals two right angles.
4. a part of a figure cut off by a line or plane intersecting it.
5. a unit of measurement of angles, one three-hundred-and-sixtieth of the circumference of a circle
7. the exact middle point of a line segment.
10. an angle of 90°, as in a corner of a square or at the intersection of two perpendicular straight lines.
12. a straight or curved continuous extent of length without breadth.
13. a person exercising government or dominion.

1. an instrument for measuring angles, typically in the form of a flat semicircle marked with degrees along the curved edge.
3. lines that meet each other at a 90 degree angle.
6. each angular point of a polygon, polyhedron, or other figure.
8. a dot or other punctuation mark, in particular a period.
9. the space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.
10. any of a set of straight lines passing through one point.
11. Two lines that never cross with each other