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]

The Collaborative International Dictionary of English v.0.48:

Harmonize \Har"mo*nize\, v. t.
   1. To adjust in fit proportions; to cause to agree; to show
      the agreement of; to reconcile the apparent contradiction
      of.
      [1913 Webster]

   2. (Mus.) To accompany with harmony; to provide with parts,
      as an air, or melody.
      [1913 Webster]

WordNet (r) 3.0 (2006):

harmonize
    v 1: go together; "The colors don't harmonize"; "Their ideas
         concorded" [syn: harmonize, harmonise, consort,
         accord, concord, fit in, agree]
    2: write a harmony for [syn: harmonize, harmonise]
    3: sing or play in harmony [syn: harmonize, harmonise]
    4: bring (several things) into consonance or relate
       harmoniously; "harmonize the different interests" [syn:
       harmonize, harmonise]
    5: bring into consonance or accord; "harmonize one's goals with
       one's abilities" [syn: harmonize, harmonise, reconcile]
    6: bring into consonance, harmony, or accord while making music
       or singing [syn: harmonize, harmonise, chord]