The Collaborative International Dictionary of English v.0.48:

Cauliflower \Cau"li*flow`er\, n. [F. choufleur, modified by E.
   Cole. L. caulis, and by E. flower; F. chou cabbage is fr. L.
   caulis stalk, cabbage, and fleur flower is fr. L. flos
   flower. See Cole, and Flower.]
   1. (Bot.) An annual variety of Brassica oleracea, or
      cabbage, of which the cluster of young flower stalks and
      buds is eaten as a vegetable.
      [1913 Webster]

   2. The edible head or "curd" of a cauliflower plant.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cauliflower
    n 1: a plant having a large edible head of crowded white flower
         buds [syn: cauliflower, Brassica oleracea botrytis]
    2: compact head of white undeveloped flowers