D defs.my
Entry 2 senses Webster, 1913

Octagon

/ŏk'təgŏn/ · Oc·ta·gon · IPA /ˈɑktəˌɡɑn/
01 n. A plane figure of eight sides and eight angles.
  1. 1.
    A plane figure of eight sides and eight angles.(Geom.)
  2. 2.
    Any structure (as a fortification) or place with eight sides or angles.
Phrases & compounds
Regular octagon — one in which the sides are all equal, and the angles also are all equal.