The Collaborative International Dictionary of English v.0.48:

dicotyledon \di*cot`y*le"don\ (d[-i]*k[o^]t`[i^]*l[=e]"d[u^]n),
   n. [Pref. di- + cotyledon.] (Bot.)
   A plant whose seeds divide into two seed lobes, or
   cotyledons, in germinating.

   Syn: dicot, dicotyl.
        [1913 Webster]

WordNet (r) 3.0 (2006):

dicotyledon
    n 1: flowering plant with two cotyledons; the stem grows by
         deposit on its outside [syn: dicot, dicotyledon,
         magnoliopsid, exogen]