Tetragonal \Te*trag"o*nal\, a.

1. (Geom.) Of or pertaining to a tetragon; having four angles or sides; thus, the square, the parallelogram, the rhombus, and the trapezium are tetragonal fingers.

2. (Bot.) Having four prominent longitudinal angles.

3. (Crystallog.) Designating, or belonging to, a certain system of crystallization; dimetric. See Tetragonal system, under Crystallization.

Source: Webster's Revised Unabridged Dictionary (1913)