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]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "attuned":
   accordant, according, agreeable, agreeing, akin, amicable,
   assonant, assonantal, at one, blended, blending, chiming,
   compatible, concordant, congenial, consonant, corresponding,
   empathetic, empathic, en rapport, frictionless, harmonic,
   harmonious, harmonizing, homophonic, in accord, in chorus,
   in concert, in concord, in rapport, in sync, in tune, in unison,
   inharmony, like-minded, monodic, monophonic, of one mind, peaceful,
   sympathetic, symphonious, synchronized, synchronous, together,
   tuned, understanding, unisonant, unisonous, united