1. Something that is opposed to some other often specified thing
2. Antonym
3. Additive inverse; especially; the additive inverse of a real number

ETYM French, from Latin oppositus, p. p. of opponere. Related to Opponent.
1. Altogether different in nature or quality or significance.
2. Being directly across from each other; facing.
3. Moving or facing away from each other.
4. The other one of a complementary pair.
5. (Botany) Of leaves etc; growing in pairs on either side of a stem; SYN. paired.

On or to an opposite side

1. Across from and usually facing or on the same level with
2. In a role complementary to