The Collaborative International Dictionary of English v.0.48:

Modification \Mod`i*fi*ca"tion\, n. [L. modificatio a measuring:
   cf. F. modification. See Modify.]
   1. The act of modifying, or the state of being modified; a
      change; as, the modification of an opinion, or of a
      machine. --Bentley.

   Syn: change, alteration, adjustment.
        [1913 Webster]

   2. Something which has been modified; a modified form or
      condition; state as modified; as, the various
      modifications of light; the latest modification of the
      operating system crashes less frequently.

   Syn: model[8].
        [1913 Webster +PJC]

   3. (Gram.) The alteration of the meaning of a word or phrase
      by another word or phrase; -- usually a restriction of the
      scope of the word modified; as, in the phrase "a billion
      dollars is a relatively small sum to spend on cancer
      research" the modification of small by relatively is
      needed to make the sentence accurate, rather than
      ludicrous.
      [PJC]

WordNet (r) 3.0 (2006):

modification
    n 1: the act of making something different (as e.g. the size of
         a garment) [syn: alteration, modification,
         adjustment]
    2: slightly modified copy; not an exact copy; "a modification of
       last year's model"
    3: the grammatical relation that exists when a word qualifies
       the meaning of the phrase [syn: modification, qualifying,
       limiting]
    4: an event that occurs when something passes from one state or
       phase to another; "the change was intended to increase
       sales"; "this storm is certainly a change for the worse";
       "the neighborhood had undergone few modifications since his
       last visit years ago" [syn: change, alteration,
       modification]

Moby Thesaurus II by Grady Ward, 1.0:

176 Moby Thesaurus words for "modification":
   about-face, accommodation, adaptation, adjustment, allophone,
   allowance, alteration, alveolar, amelioration, analysis,
   anatomization, apico-alveolar, apico-dental, apostasy,
   articulation, aspiration, assimilation, atomization, betterment,
   bilabial, break, cacuminal, cerebral, cession, change,
   change of heart, changeableness, check, circumscription,
   concession, consonant, constructive change, continuant, continuity,
   conversion, defection, degeneration, degenerative change,
   demarcation, dental, desynonymization, deterioration, deviation,
   difference, differencing, differentiation, diphthong,
   discontinuity, discrimination, disequalization, disjunction,
   dissimilation, distinction, distinguishment, divergence,
   diversification, diversion, diversity, division, epenthetic vowel,
   exception, exemption, explosive, extenuating circumstances,
   fitting, flip-flop, glide, glottal, glottalization, gradual change,
   grain of salt, grant, guttural, hedge, hedging, improvement,
   individualization, individuation, labial, labialization,
   labiodental, labiovelar, laryngeal, lateral, limitation, lingual,
   liquid, manner of articulation, melioration, mental reservation,
   metamorphosis, mitigation, modulation, monophthong, morphophoneme,
   mutation, mute, nasal, occlusive, overthrow, palatal,
   parasitic vowel, particularization, peak, personalization,
   pharyngeal, pharyngealization, phone, phoneme, plosive,
   prothetic vowel, qualification, radical change, re-creation,
   realignment, redesign, reform, reformation, remaking, renewal,
   reservation, reshaping, restriction, restructuring, retroflex,
   reversal, revival, revivification, revolution, salvo,
   segmental phoneme, segregation, semivowel, separation,
   severalization, severance, shift, sonant, sonority, special case,
   special treatment, specialization, specialness, specification,
   speech sound, stop, sudden change, surd, switch, syllabic nucleus,
   syllabic peak, syllable, tempering, total change, transformation,
   transition, transition sound, transmogrification, triphthong, turn,
   turnabout, upheaval, variation, variety, velar, violent change,
   vocable, vocalic, vocoid, voice, voiced sound, voiceless sound,
   voicing, vowel, waiver, worsening



Bouvier's Law Dictionary, Revised 6th Ed (1856):

MODIFICATION. A change; as the modification of a contract. This may take
place at the time of making the contract by a condition, which shall have
that effect; for example, if I sell you one thousand bushels of corn, upon
condition that any crop shall produce that much, and it produces only eight
hundred bushels, the contract is modified, it is for eight hundred bushels,
and no more.
     2. It may be modified by the consent of both parties, after it has been
made. See 1 Bouv. Inst. n. 733.