octagon

noun

1. (also, attributive)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; [...]”

   “Bismuth is the most common of all native metallic substances. It is generally found either in cubes or octagons, or of a dendritical form, or else in thin laminæ investing the ores of other metals, particularly those of cobalt.”

   “The font is an octagon, having at each angle a slender pillar with crockets and finials, and the sides are richly sculptured with angels and animals, the figures holding shields, with various devices; at each corner of the contracting part towards the pedestal, are cherubs heads with expanded wings; and the pedestal, which is an irregular octagon, is ornamented with four non-descript animals, scaled over their breasts; on a moulding round the bottom are several old characters, now illegible.”

   “The building [the Winter Garden conservatory, Kew Gardens] was to be of five parts—a centre, two small octagons, and two wings connected by the octagons with the centre. The centre and the two octagons were finished, and some expenditure must have been laid out on the wings, as the ground was dug out and foundations in concrete laid for the pillars.”

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