The Collaborative International Dictionary of English v.0.48:

Adaptation \Ad`ap*ta"tion\, n. [Cf. F. adaptation, LL.
   adaptatio.]
   1. The act or process of adapting, or fitting; or the state
      of being adapted or fitted; fitness. "Adaptation of the
      means to the end." --Erskine.
      [1913 Webster]

   2. The result of adapting; an adapted form.
      [1913 Webster]

WordNet (r) 3.0 (2006):

adaptation
    n 1: a written work (as a novel) that has been recast in a new
         form; "the play is an adaptation of a short novel" [syn:
         adaptation, version]
    2: the process of adapting to something (such as environmental
       conditions) [syn: adaptation, adaption, adjustment]
    3: (physiology) the responsive adjustment of a sense organ (as
       the eye) to varying conditions (as of light)

Moby Thesaurus II by Grady Ward, 1.0:

164 Moby Thesaurus words for "adaptation":
   Nachtmusik, about-face, absolute music, accommodation, accord,
   accordance, acquiescence, adaption, adjusting, adjustment,
   agreement, air varie, aleatory, aleatory music, alignment,
   alteration, amelioration, apostasy, arrangement, assimilation,
   attunement, bearings, betterment, biological evolution, break,
   chamber music, chamber orchestra, change, change of heart,
   changeableness, coaptation, compliance, composition, conditioning,
   conformance, conformation other-direction, conformity, congruity,
   consistency, constructive change, continuity, conventionality,
   conversion, coordination, correspondence, defection, degeneration,
   degenerative change, descant, deterioration, deviation, difference,
   discontinuity, disorientation, divergence, diversification,
   diversion, diversity, electronic music, enablement, equipment,
   etude, exercise, fit, fitting, flexibility, flip-flop, furnishing,
   genesis, gradual change, harmonization, harmony, horotely,
   improvement, incidental music, instrumental music, instrumentation,
   integration, intonation, invention, keeping, line, malleability,
   melioration, mitigation, modification, modifying, modulation,
   natural selection, nocturne, obedience, observance, ontogenesis,
   ontogeny, opus, orchestration, orientation, orthodoxy, overthrow,
   phrasing, phylogenesis, phylogeny, physiogenesis, physiogeny,
   piece, pliancy, preparation, production, program music,
   qualification, radical change, re-creation, realignment,
   reconcilement, reconciliation, redesign, reform, reformation,
   regulation, remaking, renewal, reshaping, resolution,
   restructuring, reversal, revival, revivification, revolution,
   ricercar, score, setting, shift, solution, sonata, sonatina,
   squaring, strictness, string orchestra, string quartet, study,
   sudden change, suiting, suspension, switch, synchronization,
   tachytely, theme and variations, timing, tone painting,
   total change, traditionalism, transcription, transition, trio,
   tuning, turn, turnabout, uniformity, upheaval, variation, variety,
   violent change, work, worsening