1. (

• basis ,
• base ,
• foundation ,
• fundament ,
• groundwork ,
• cornerstone

) the fundamental assumptions from which something is begun or developed or calculated or explained; "the whole argument rested on a basis of conjecture" ;

2. (

• buttocks ,
• nates ,
• arse ,
• butt ,
• backside ,
• bum ,
• buns ,
• can ,
• fundament ,
• hindquarters ,
• hind_end ,
• keister ,
• posterior ,
• prat ,
• rear ,
• rear_end ,
• rump ,
• stern ,
• seat ,
• tail ,
• tail_end ,
• tooshie ,
• tush ,
• bottom ,
• behind ,
• derriere ,
• fanny ,
• ass

) the fleshy part of the human body that you sit on; "he deserves a good kick in the butt"; "are you going to sit on your fanny and do nothing?" ;

3. (

• foundation ,
• base ,
• fundament ,
• foot ,
• groundwork ,
• substructure ,
• understructure

) lowest support of a structure; "it was built on a base of solid rock"; "he stood at the foot of the tower" ;