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:

Decompose \De`com*pose"\, v. i.
   To become resolved or returned from existing combinations; to
   undergo dissolution; to decay; to rot.
   [1913 Webster]

WordNet (r) 3.0 (2006):

decompose
    v 1: separate (substances) into constituent elements or parts
         [syn: decompose, break up, break down]
    2: lose a stored charge, magnetic flux, or current; "the
       particles disintegrated during the nuclear fission process"
       [syn: disintegrate, decay, decompose]
    3: break down; "The bodies decomposed in the heat" [syn:
       decompose, rot, molder, moulder]