The Collaborative International Dictionary of English v.0.48:

Subcontract \Sub*con"tract\, n.
   A contract under, or subordinate to, a previous contract.
   [1913 Webster]

WordNet (r) 3.0 (2006):

subcontract
    n 1: a contract assigning to another party some obligations of a
         prior contract
    v 1: arranged for contracted work to be done by others [syn:
         subcontract, farm out, job]
    2: work under a subcontract; engage in a subcontract