The Collaborative International Dictionary of English v.0.48:
Substruction \Sub*struc"tion\, n. [L. substructio, fr. substruere, substructum, to build beneath; sub under + struere to build.] (Arch.) Underbuilding; the foundation, or any preliminary structure intended to raise the lower floor or basement of a building above the natural level of the ground. [1913 Webster] It is a magnificent strong building, with a substruction very remarkable. --Evelyn. [1913 Webster]