Source : Webster's Revised Unabridged Dictionary (1913)

Tetragon \Tet"ra*gon\, n. [L. tetragonum, Gr. tetra`gwnon;
   te`tra- (see {Tetra-}) + gwni`a corner, angle: cf. F.
   t['e]tragone.]
   1. (Geom.) A plane figure having four sides and angles; a
      quadrangle, as a square, a rhombus, etc.

   2. (Astrol.) An aspect of two planets with regard to the
      earth when they are distant from each other ninety
      degrees, or the fourth of a circle. --Hutton.

Source : WordNet®

tetragon
     n : a four-sided polygon [syn: {quadrilateral}, {quadrangle}]