Source : Webster's Revised Unabridged Dictionary (1913)

Substructure \Sub*struc"ture\, n. [Pref. sub- + structure.]
   1. (Arch.) Same as {Substruction}.

   2. An under structure; a foundation; groundwork.

Source : WordNet®

substructure
     n 1: the basic structure or features of a system or organization
          [syn: {infrastructure}]
     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}, {understructure}]