The Collaborative International Dictionary of English v.0.48:

Polymer \Pol"y*mer\, n. [See Polymeric.] (Chem.)
   Any one of two or more substances related to each other by
   polymerism; specifically, a substance produced from another
   substance by chemical polymerization. [Formerly also written
   polymere.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

polymer
    n 1: a naturally occurring or synthetic compound consisting of
         large molecules made up of a linked series of repeated
         simple monomers