The Collaborative International Dictionary of English v.0.48:

Decompose \De`com*pose"\, v. t. [imp. & p. p. Decomposed; p.
   pr. & vb. n. Decomposing.] [Cf. F. d['e]composer. Cf.
   Discompose.]
   To separate the constituent parts of; to resolve into
   original elements; to set free from previously existing forms
   of chemical combination; to bring to dissolution; to rot or
   decay.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decomposed \De`com*posed"\, a. (Zool.)
   Separated or broken up; -- said of the crest of birds when
   the feathers are divergent.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "decomposed":
   bad, cankered, carious, corrupt, decayed, festering, foul,
   gangrened, gangrenous, gone bad, mortified, necrosed, necrotic,
   peccant, putrefied, putrescent, putrid, rotten, rotting,
   sphacelated, spoiled, suppurating, suppurative, ulcerated