regular octagon

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]