The Collaborative International Dictionary of English v.0.48:

Groundwork \Ground"work`\ (ground"w[^u]rk`), n.
   That which forms the foundation or support of anything; the
   basis; the essential or fundamental part; first principle;
   as, development of a convenient DNA sequencing technique
   layed the groundwork for many of the subsequent advances in
   molecular genetics. --Dryden.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

groundwork
    n 1: the fundamental assumptions from which something is begun
         or developed or calculated or explained; "the whole
         argument rested on a basis of conjecture" [syn: basis,
         base, foundation, fundament, groundwork,
         cornerstone]
    2: lowest support of a structure; "it was built on a base of
       solid rock"; "he stood at the foot of the tower" [syn:
       foundation, base, fundament, foot, groundwork,
       substructure, understructure]
    3: preliminary preparation as a basis or foundation; "we are
       prepared today because of groundwork that was done ten years
       ago"