THESAURUS
base, baseboard, basement, bedrock, bottom, chassis, dado, foot, footing, foundation, frame, keel, lower strata, lowest level, lowest point, mopboard, shoemold, sole, toe, underlying level, wainscot
ROGET THESAURUS
Base
N
base, basement, plinth, dado, wainscot, baseboard, mopboard, bedrock, hardpan, foundation, substructure, substratum, ground, earth, pavement, floor, paving, flag, carped, ground floor, deck, footing, ground work, basis, hold, bilge, bottom,
nadir, foot, sole, toe, hoof, keel, root, centerboard, bottom, undermost, nethermost, fundamental, founded on, based on, grounded on, built on.