The Collaborative International Dictionary of English v.0.48:

Centaurea \Cen`tau*re"a\, prop. n. [NL. See Centaury.] (Bot.)
   A large genus of composite plants, related to the thistles
   and including the cornflower or bluebottle (Centaurea
   Cyanus) and the star thistle (Centaurea Calcitrapa).
   [1913 Webster]

WordNet (r) 3.0 (2006):

Centaurea
    n 1: knapweed; star thistle [syn: Centaurea, genus
         Centaurea]