Synonyms and related words :
backside, base, basement, basis, beam, bearing wall, bed, bedding, bedrock, behind, belly, bottom, bottom side, breech, buttocks, derriere, downside, floor, flooring, fond, footing, foundation, fundamental, ground, grounds, groundwork, hardpan, lower side, lowest layer, lowest level, nether side, nethermost level, pavement, posterior, principle, radical, rear, riprap, rock bottom, rudiment, rump, seat, sill, solid ground, solid rock, stereobate, stylobate, substratum, substruction, substructure, terra firma, underbelly, underbuilding, undercarriage, undergirding, underlayer, underneath, underpinning, underside, understruction, understructure