THESAURUS
base, basement, basis, bearing wall, bed, bedding, bedrock, bottom, floor, flooring, fond, footing, foundation, fundament, fundamental, ground, grounds, groundwork, hardpan, infrastructure, pavement, principle, radical, riprap, rock bottom, rudiment, seat, sill, solid ground, solid rock, stereobate, stylobate, substratum, substruction, terra firma, underbuilding, undercarriage, undergirding, underpinning, understruction, understructure
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.