Source : Webster's Revised Unabridged Dictionary (1913)

Dicotyledonous \Di*cot`y*le"don*ous\, a. (Bot.)
   Having two cotyledons or seed lobes; as, a dicotyledonous
   plant.

Source : WordNet®

dicotyledonous
     adj : (of a flowering plant) having two cotyledons in the seed
           [ant: {monocotyledonous}]