bottom n
1 base, basis, bed, deepest part, depths, floor, foot, foundation, groundwork, lowest part, pedestal, support
2 lower side, sole, underneath, underside
3 arse (taboo slang) ass (U.S. & Canad. taboo slang) backside, behind (informal) bum (Brit. slang) buns (U.S. slang) butt (U.S. & Canad. informal) buttocks, derrière (euphemistic) fundament, jacksy (Brit. slang) posterior, rear, rear end, rump, seat, tail (informal) tush (U.S. slang)
4 base, basis, cause, core, essence, ground, heart, mainspring, origin, principle, root, source, substance adj
5 base, basement, basic, fundamental, ground, last, lowest, undermost n
1 & 2 cover, crown, height, lid, peak, summit, surface, top adj higher, highest, top, upper