fundament

[1]	basis , base , foundation , groundwork , cornerstone
[2]	buttocks , nates , arse , butt , backside , bum , buns , can , hindquarters , hind end , keister , posterior , prat , rear , rear end , rump , stern , seat , tail , tail end , tooshie , tush , bottom , behind , derriere , fanny , ass
[3]	foundation , base , foot , groundwork , substructure , understructure