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]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "dicotyledon":
   Angiospermae, Cycadales, Ginkgoales, Gnetales, Monocotyledones,
   Pinales, amphibian, angiosperm, angiosperms, annual, aquatic plant,
   biennial, conifers, cosmopolite, cutting, cycads, deciduous plant,
   dicot, dicotyledons, endogens, ephemeral, evergreen, exotic,
   flowering plant, fungus, gametophyte, ginkgoes, gnetums,
   gymnosperm, gymnosperms, hydrophyte, monocot, monocotyl,
   monocotyledons, perennial, plant, polycot, polycotyl,
   polycotyledon, seed plant, seedling, spermatophyte, sporophyte,
   thallophyte, triennial, vascular plant, vegetable, weed