The Collaborative International Dictionary
Polygon \Pol"y*gon\, n. [Gr. poly`gwnos polygonal; poly`s many + gwni`a angle: cf. F. polygone.] (Geom.) A plane figure having many angles, and consequently many sides; esp., one whose perimeter consists of more than four sides; any figure having many angles.
Polygon of forces (Mech.), a polygonal figure, the sides of which, taken successively, represent, in length and direction, several forces acting simultaneously upon one point, so that the side necessary to complete the figure represents the resultant of those forces. Cf. Parallelogram of forces, under Parallelogram.
Wiktionary
n. (context mechanics English) A polygonal figure the sides of which are vectors representing several forces acting simultaneously upon one point, so that the vector necessary to make the figure closed is the resultant of those forces.