Source : Webster's Revised Unabridged Dictionary (1913)

Monopetalous \Mon`o*pet"al*ous\, a. [Mono- + petal: cf. F.
   monop['e]tale.] (Bot.)
   Having only one petal, or the corolla in one piece, or
   composed of petals cohering so as to form a tube or bowl;
   gamopetalous.

   Note: The most recent authors restrict this form to flowers
         having a solitary petal, as in species of {Amorpha},
         and use {gamopetalous} for a corolla of several petals
         combined into one piece. See Illust. of {Gamopetalous}.