The Collaborative International Dictionary of English v.0.48:

Decompound \De`com*pound"\, v. t. [imp. & p. p. Decompounded;
   p. pr. & vb. n. Decompounding.] [Pref. de- (intens. in
   sense 1) + compound, v. t.]
   1. To compound or mix with that is already compound; to
      compound a second time.
      [1913 Webster]

   2. To reduce to constituent parts; to decompose.
      [1913 Webster]

            It divides and decompounds objects into . . . parts.
                                                  --Hazlitt.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decompound \De`com*pound"\, a. [Pref. de- (intens.) + compound,
   a.]
   1. Compound of what is already compounded; compounded a
      second time.
      [1913 Webster]

   2. (Bot.) Several times compounded or divided, as a leaf or
      stem; decomposite.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decompound \De`com*pound"\, n.
   A decomposite.
   [1913 Webster]

WordNet (r) 3.0 (2006):

decompound
    adj 1: of a compound leaf; consisting of divisions that are
           themselves compound