Synonyms and related words :
band, bed, bedding, bedrock, belly, belt, bottom, bottom side, breech, buttocks, couche, course, deck, downside, floor, fundament, gallery, hardpan, layer, ledge, level, lower side, lowest layer, lowest level, measures, nether side, nethermost level, overlayer, overstory, rock bottom, seam, shelf, stage, step, story, stratum, substratum, superstratum, thickness, tier, topsoil, underbelly, underneath, underside, understory, understratum, zone