The Collaborative International Dictionary of English v.0.48:

Cymatium \Cy*ma"ti*um\ (s?-m?"sh?-?m), n. [L., fr. Gr. ?????,
   dim. of ???? a wave.] (Arch.)
   A capping or crowning molding in classic architecture.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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