From The Collaborative International Dictionary of English v.0.48 [gcide]:
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]
From WordNet (r) 3.0 (2006) [wn]:
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