The Collaborative International Dictionary of English v.0.48:

Symphonize \Sym"pho*nize\, v. i. [imp. & p. p. Symphonized; p.
   pr. & vb. n. Symphonizing.]
   To agree; to be in harmony. [R.] --Boyle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

symphonize
    v 1: play or sound together, in harmony [syn: symphonize,
         symphonise]