'Pentagon' definitions:

Definition of 'Pentagon'

From: WordNet
noun
A government building with five sides that serves as the headquarters of the United States Department of Defense
noun
The United States military establishment
noun
A five-sided polygon

Definition of 'Pentagon'

From: GCIDE
  • Pentagon \Pen"ta*gon\, n. [Gr. penta`gwnon; penta- (see Penta-) + gwni`a angle: cf. L. pentagonium, F. pentagone.] (Geom.) A plane figure having five angles, and, consequently, five sides; any figure having five angles. [1913 Webster]
  • Regular pentagon, a pentagon in which the angles are all equal, and the sides all equal. [1913 Webster]