offside

adjective, adverb

1. Sports. illegally beyond a prescribed line or area or in advance of the ball or puck at the beginning of or during play or a play: The touchdown was nullified because the offensive left tackle was offside.
2. with or in doubtful propriety or taste; risqué: an offside joke.

adjective, adverb

1. sport (in football, hockey, etc) in a position illegally ahead of the ball or puck when it is played, usually when within one’s opponents’ half or the attacking zone

noun

2. the offside mainly British
   1. the side of a vehicle nearest the centre of the road (in Britain, the right side)
   2. (as modifier)the offside passenger door

also off-side, 1867, in various sporting senses, originally in English football; from off + side (n.).