pentagon

from WordNet (r) 3.0 (2006)

Pentagon
    n 1: a government building with five sides that serves as the
         headquarters of the United States Department of Defense
    2: the United States military establishment
    3: a five-sided polygon

from The Collaborative International Dictionary of English v.0.48

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]

from U.S. Gazetteer (1990)

Pentagon, DC
  Zip code(s): 20301