GNU Dico
From WordNet dictionary, version 3.0:
behind
n. 1. 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?"
Synonyms: 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, derriere, fanny, ass
s. 1. having the lower score or lagging position in a contest; "behind by two points"; "the 8th inning found the home team trailing"
r. 1. in or to or toward the rear; "he followed behind"; "seen from behind, the house is more imposing than it is from the front"; "the final runners were far behind"
2. remaining in a place or condition that has been left or departed from; "when he died he left much unfinished work behind"; "left a large family behind"; "the children left their books behind"; "he took off with a squeal of tires and left the other cars far behind"
3. of timepieces; "the clock is almost an hour slow"; "my watch is running behind"
Synonyms: slow
4. in or into an inferior position; "fell behind in his studies"; "their business was lagging behind in the competition for customers"
5. in debt; "he fell behind with his mortgage payments"; "a month behind in the rent"; "a company that has been run behindhand for years"; "in arrears with their utility bills"
Synonyms: behindhand, in arrears