The Collaborative International Dictionary of English v.0.48:

Cyma \Cy"ma\ (s[imac]"m[.a]) n. [NL., fr. Gr. ky^ma See Cyme]
   [1913 Webster]
   1. (Arch.) A member or molding of the cornice, the profile of
      which is wavelike in form.
      [1913 Webster]

   2. (Bot.) A cyme. See Cyme.
      [1913 Webster]

   Cyma recta, or Cyma, a cyma, hollow in its upper part and
      swelling below.

   Cyma reversa, or Cyma Ogee, a cyma swelling out on the
      upper part and hollow below.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cyma
    n 1: (architecture) a molding for a cornice; in profile it is
         shaped like an S (partly concave and partly convex) [syn:
         cyma, cymatium]