The Collaborative International Dictionary of English v.0.48:

Cyme \Cyme\ (s?m), n. [L. cyma the young sprount of a cabbage,
   fr. Gr. ???, prop., anything swollen, hence also cyme, wave,
   fr. ??? to be pregnant.] (Bot.)
   A flattish or convex flower cluster, of the centrifugal or
   determinate type, differing from a corymb chiefly in the
   order of the opening of the blossoms.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cyme
    n 1: more or less flat-topped cluster of flowers in which the
         central or terminal flower opens first