The Collaborative International Dictionary of English v.0.48:

Degeneration \De*gen`er*a"tion\, n. [Cf. F.
   d['e]g['e]n['e]ration.]
   1. The act or state of growing worse, or the state of having
      become worse; decline; degradation; debasement;
      degeneracy; deterioration.
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            Our degeneration and apostasy.        --Bates.
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   2. (Physiol.) That condition of a tissue or an organ in which
      its vitality has become either diminished or perverted; a
      substitution of a lower for a higher form of structure;
      as, fatty degeneration of the liver.
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   3. (Biol.) A gradual deterioration, from natural causes, of
      any class of animals or plants or any particular organ or
      organs; hereditary degradation of type.
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   4. The thing degenerated. [R.]
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            Cockle, aracus, . . . and other degenerations. --Sir
                                                  T. Browne.
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   Amyloid degeneration, Caseous degeneration, etc. See
      under Amyloid, Caseous, etc.
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WordNet (r) 3.0 (2006):

degeneration
    n 1: the process of declining from a higher to a lower level of
         effective power or vitality or essential quality [syn:
         degeneration, devolution] [ant: development,
         evolution]
    2: the state of being degenerate in mental or moral qualities
       [syn: degeneracy, degeneration, decadence, decadency]
    3: passing from a more complex to a simpler biological form
       [syn: degeneration, retrogression]

Moby Thesaurus II by Grady Ward, 1.0:

131 Moby Thesaurus words for "degeneration":
   abandon, abandonment, abjection, about-face, accommodation,
   adaptation, adjustment, alteration, amelioration, apostasy,
   atrophy, betterment, break, change, change of heart,
   changeableness, closed loop, closed sequence, comedown,
   constructive change, continuity, conversion, corruptedness,
   corruption, corruptness, current-control circuit, debasement,
   decadence, decadency, declension, declination, decline, defection,
   deformation, degeneracy, degenerateness, degenerative change,
   degradation, demoralization, demotion, depravation, depravedness,
   depravity, depreciation, derogation, descent, deterioration,
   deviation, devolution, difference, discontinuity, dissoluteness,
   divergence, diversification, diversion, diversity, downfall,
   downgrade, downtrend, downturn, downward mobility, downward trend,
   drop, dying, ebb, effeteness, fading, failing, failure,
   failure of nerve, fall, falling-off, feedback, fitting, flip-flop,
   flip-flop circuit, gradual change, improvement, involution, lapse,
   loss of tone, melioration, mitigation, modification, modulation,
   moral pollution, moral turpitude, overthrow, perversion,
   positive feedback, process loop, profligacy, qualification,
   quality loop, radical change, re-creation, realignment, redesign,
   reform, reformation, regression, remaking, renewal, reprobacy,
   reshaping, restructuring, retrocession, retrogradation,
   retrogression, reversal, reversed feedback, revival,
   revivification, revolution, rottenness, shift, slippage, slump,
   sudden change, switch, total change, transition, turn, turnabout,
   turpitude, upheaval, variation, variety, violent change, wane,
   worsening