octagon

noun

Etymology: From Latin octagōnon, octōgōnon (“octagon”), and from its etymon Ancient Greek ὀκτάγωνον (oktágōnon, “octagon”), probably from Koine Greek ὀκτάγωνος (oktágōnos, “having eight corners”) + -ον (-on, suffix forming nouns). ὀκτάγωνος is derived from ὀκτᾰ- (oktă-, prefix meaning ‘eight’) (from ὀκτώ (oktṓ, “eight”), ultimately from Proto-Indo-European *oḱtṓw (“eight”)) + γωνία (gōnía, “angle; corner”) (probably ultimately from Proto-Indo-European *ǵónu (“knee”)); analysable as octa- + -gon. The English word is cognate with Middle French octogone (modern French octogone), Italian octagono (obsolete), ottagono, Spanish octágono, octógono. Sense 2 (“arena for mixed martial arts”) refers to its shape.

1. A polygon with eight sides and eight angles.

   “From the Circle deſcribe the Octagon, by taking half the Quadrant of the former for each Side of the latter. [...] [B]y conjoining theſe Points with ſtrait Lines agreeable to the Shape of the Octagon, the whole Work is completed.”

   “In like manner it is demonſtrated that one angle of a regular hexagon will be equal to one right angle, and one third part of one right angle; one angle of a regular octagon equal to one right angle and half a right angle; [...]”

2. Often in the form Octagon: the arena for mixed martial arts.