The Collaborative International Dictionary of English v.0.48:

Centaury \Cen"tau*ry\ (s[e^]n"t[add]*r[y^]), n. [L. centaureum
   and centauria, Gr. kentay`rion, kentay`reion, and kentayri`h,
   fr. the Centaur Chiron.] (Bot.)
   A gentianaceous plant not fully identified. The name is
   usually given to the Eryther[ae]a Centaurium and the
   Chlora perfoliata of Europe, but is also extended to the
   whole genus Sabbatia, and even to the unrelated
   Centaurea.
   [1913 Webster]

WordNet (r) 3.0 (2006):

centaury
    n 1: any of various plants of the genus Centaurium
    2: any plant of the genus Centaurea