gon-, gonio-, -gon, -gonal, -gonally, -gony

(Greek: corner, bend, angle)

oxygon
Having acute angles; acute-angled.
pentagon, Pentagon
1. A shape with five sides, usually of equal length, and angles greater than 90°.
2. A two-dimensional geometric figure formed of five sides and five angles.
3. When capitalized, it is the government building in Washington, D.C. with five sides which serves as the headquarters of the United States Department of Defense.

The Pentagon houses the main offices for the armed services of the United States and the military personnel who work in this building.

polygon
A geometrical plane figure with three or more straight sides; a figure of many angles.
tetragon
trigon
1. A figure having three angles and three sides; a triangle.
2. A set of three signs of the zodiac, distant 120 degrees from each other, as if at the angles of an equilateral triangle.
trigonometry
That branch of mathematics that deals with the measurement of the sides and angles of triangles, particularly with certain functions of their angles or of angles in general (the sine, cosine, tangent, cotangent, secant, and cosecant), and hence with these functions as applied to abstract quantities; thus including the theory of triangles, of angles, and of (elementary) singly periodic functions.