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From The Collaborative International Dictionary of English v.0.48:
Octagon \Oc"ta*gon\, n. [Gr. ? eight-cornered; 'okta- (for 'oktw` eight) + ? an angle: cf. F. cctogone.] 1. (Geom.) A plane figure of eight sides and eight angles. [1913 Webster] 2. Any structure (as a fortification) or place with eight sides or angles. [1913 Webster] Regular octagon, one in which the sides are all equal, and the angles also are all equal. [1913 Webster]