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 reversa
    n 1: a molding that (in section) has the shape of an S with the
         convex part above and the concave part below [syn: ogee,
         cyma reversa]