Source : Webster's Revised Unabridged Dictionary (1913)

Trapezoidal \Trap`e*zoid"al\, a. [Cf. F. trap['e]zo["i]dal.]
   1. Having the form of a trapezoid; trapezoid.

   2. (Min.) Trapezohedral.

Source : WordNet®

trapezoidal
     adj : resembling a trapezoid