The Collaborative International Dictionary of English v.0.48:

Polysynthesis \Pol`y*syn"the*sis\, n. [Poly- + synthesis.]
   1. The act or process of combining many separate elements
      into a whole.
      [1913 Webster]

   2. (Philol.) The formation of a word by the combination of
      several simple words, as in the aboriginal languages of
      America; agglutination. --Latham.
      [1913 Webster]