The Collaborative International Dictionary of English v.0.48:

Synthesis \Syn"the*sis\, n.; pl. Syntheses. [L., a mixture,
   properly, a putting together, Gr. ?, fr. ? to place or put
   together; sy`n with + ? to place. See Thesis.]
   1. Composition, or the putting of two or more things
      together, as in compounding medicines.
      [1913 Webster]

   2. (Chem.) The art or process of making a compound by putting
      the ingredients together, as contrasted with analysis;
      thus, water is made by synthesis from hydrogen and oxygen;
      hence, specifically, the building up of complex compounds
      by special reactions, whereby their component radicals are
      so grouped that the resulting substances are identical in
      every respect with the natural articles when such occur;
      thus, artificial alcohol, urea, indigo blue, alizarin,
      etc., are made by synthesis.
      [1913 Webster]

   3. (Logic) The combination of separate elements of thought
      into a whole, as of simple into complex conceptions,
      species into genera, individual propositions into systems;
      -- the opposite of analysis.
      [1913 Webster]

            Analysis and synthesis, though commonly treated as
            two different methods, are, if properly understood,
            only the two necessary parts of the same method.
            Each is the relative and correlative of the other.
                                                  --Sir W.
                                                  Hamilton.
      [1913 Webster]