1. <geometry> A plane figure having four sides and angles; a quadrangle, as a square, a rhombus, etc.

2. <astronomy> 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.

Origin: L. Tetragonum, Gr.; (see Tetra-) + corner, angle: cf. F. Tetragone.

(01 Mar 1998)