The Collaborative International Dictionary of English v.0.48:

Harmonize \Har"mo*nize\ (h[aum]r"m[-o]*n[imac]z), v. i. [imp. &
   p. p. Harmonized (-n[imac]zd); p. pr. & vb. n.
   Harmonizing (-n[imac]"z[i^]ng).] [Cf. F. harmoniser. ]
   1. To agree in action, adaptation, or effect on the mind; to
      agree in sense or purport; as, the parts of a mechanism
      harmonize.
      [1913 Webster]

   2. To be in peace and friendship, as individuals, families,
      or public organizations.
      [1913 Webster]

   3. To agree in vocal or musical effect; to form a concord;
      as, the tones harmonize perfectly.
      [1913 Webster]