n. 八边形, 八角形

[ noun ]
an eight-sided polygon
<noun.shape>

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.

2. Any structure (as a fortification) or place with eight
sides or angles.

{Regular octagon}, one in which the sides are all equal, and
the angles also are all equal.