[1] : The Collaborative International Dictionary of English v.0.48

decadence \deca"dence\, decadency \deca"dency\, n. ll.
   decadentia; l. de- + cadere to fall: cf. f. d'ecadence. see
   decay.
   a falling away; decay; deterioration; declension. "the old
   castle, where the family lived in their decadence." --sir w.
   scott.
   1913 webster
see also:
decay 

[2] : WordNet (r) 2.0

decadence
     n : the state of being degenerate in mental or moral qualities
         syn: degeneracy, degeneration, decadency
see also:
degeneracy degeneration decadency 

[3] : Moby Thesaurus II by Grady Ward, 1.0

65 moby thesaurus words for "decadence":
   abandon, abandonment, abjection, comedown, corruptedness,
   corruption, corruptness, debasement, decadency, decadent, decayed,
   declension, declination, decline, deformation, degeneracy,
   degenerate, degenerateness, degeneration, degradation,
   demoralization, demotion, depravation, depravedness, depravity,
   depreciation, derogation, descent, deterioration, devolution,
   dissoluteness, downfall, downgrade, downtrend, downturn,
   downward mobility, downward trend, drop, dying, ebb, effeteness,
   fading, failing, failure, failure of nerve, fall, falling-off,
   involution, lapse, loss of tone, moral pollution, moral turpitude,
   overripe, profligacy, regress, regression, reprobacy, retrocession,
   retrogradation, retrogression, rottenness, slippage, slump,
   turpitude, wane

Decadence >> D Words
Decadence, definition of term: Decadence
decadence_pag1.html