Source : Webster's Revised Unabridged Dictionary (1913)

Monocotyledonous \Mon`o*cot`y*le"don*ous\, a. [Cf. F.
   monocotyl['e]don['e].] (Bot.)
   Having only one cotyledon, seed lobe, or seminal leaf.
   --Lindley.

Source : WordNet®

monocotyledonous
     adj : (of a flowering plant) having a single cotyledon in the seed
           as in grasses and lilies [ant: {dicotyledonous}]