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]

Moby Thesaurus II by Grady Ward, 1.0:

251 Moby Thesaurus words for "harmonize":
   accommodate, accommodate with, accord, act in concert,
   act together, adapt, adapt to, adjust, adjust to, affiliate, agree,
   agree with, ally, amalgamate, answer to, arrange, arrange matters,
   array, assent, assimilate, assimilate to, associate, assonate,
   assort with, atone, attune, balance, band, band together,
   be consistent, be guided by, be harmonious, be in cahoots,
   be in league, be in tune, be of one, be uniform with, bend, blend,
   bring to terms, bring together, chart, check, chime, chime in with,
   chord, club together, coact, coadunate, coalesce, codify, cohere,
   coincide, collaborate, collude, combine, comply, comply with,
   compose, compromise, concert, concord, concur, confederate,
   conform, conform with, conjoin, connive, consist with, consolidate,
   conspire, cool off, cooperate, coordinate, correct, correlate,
   correspond, cotton to, cut to, damp, deploy, discipline, dispose,
   do business with, dovetail, empathize, equalize, equilibrize, even,
   even up, fall in together, fall in with, federate, fit, fit in,
   fit together, fix, fix up, flatten, follow, form, fuse, gear to,
   get along, get along with, get heads together, get on with,
   get together, go, go by, go partners, go together, go with, grade,
   hang together, happen together, harmonize with, heal the breach,
   hierarchize, hit, hold together, homogenize, homologate,
   homologize, hook up, identify with, instrument, instrumentate,
   integrate, interchange, interlock, intersect, jibe, join, join in,
   join together, keep together, key to, lay out, league,
   league together, level, line up, lock, make an adaptation,
   make common cause, make conform, make plumb, make uniform, marshal,
   match, measure, mediate, meet, melodize, merge, methodize, mold,
   musicalize, normalize, observe, orchestrate, order, organize,
   overlap, pacify, parallel, partner, patch things up, plan,
   play ball, proportion, proportionate, pull together,
   put heads together, put in tune, put to music, quiet, rank,
   rationalize, reciprocate, reconcile, rectify, register,
   register with, regularize, regulate, relate, resolve, respond to,
   restore harmony, reunite, right, routinize, rub off corners, score,
   set, set right, set to music, set up, settle, settle differences,
   shape, similarize, sing in chorus, smooth, smooth it over,
   sort with, sound in tune, sound together, square, square with,
   stabilize, stand together, standardize, stereotype, straighten,
   structure, suit, symmetrize, sympathize, symphonize, sync,
   synchronize, synergize, synthesize, systematize, tailor, tally,
   tally with, team up, throw in together, tie in, tie up,
   tranquilize, transcribe, transpose, trim to, true, true up, tune,
   tune up, understand one another, uniformize, unify, unite,
   unite efforts, weave peace between, work together, write, yield