The Collaborative International Dictionary of English v.0.48:

Attune \At*tune"\, v. t. [imp. & p. p. Attuned; p. pr. & vb.
   n. Attuning.] [Pref. ad- + tune.]
   [1913 Webster]
   1. To tune or put in tune; to make melodious; to adjust, as
      one sound or musical instrument to another; as, to attune
      the voice to a harp.
      [1913 Webster]

   2. To arrange fitly; to make accordant.
      [1913 Webster]

            Wake to energy each social aim,
            Attuned spontaneous to the will of Jove. --Beattie.
      [1913 Webster]

WordNet (r) 3.0 (2006):

attune
    v 1: adjust or accustom to; bring into harmony with

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "attune":
   accommodate, accord, adapt, adjust, adjust to, agree, assimilate,
   assonate, atone, balance, be harmonious, be in tune, blend,
   capacitate, chime, chord, compensate, condition, conform,
   coordinate, counterbalance, cut to, enable, equalize, equip, fit,
   fix, furnish, gear to, harmonize, homologate, homologize,
   integrate, key to, make plumb, make uniform, measure, melodize,
   musicalize, proportion, put in trim, put in tune, qualify,
   reconcile, rectify, regulate, right, set, set right, set to rights,
   similarize, sound in tune, sound together, string, suit,
   symphonize, sync, synchronize, tailor, tone down, tone up, trim to,
   true, true up, tune, tune up, voice