Wordnet 3.0
NOUN (1)
1.
an eight-sided polygon;
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]
WordNet (r) 3.0 (2006):
octagon
n 1: an eight-sided polygon