noun

1. the act of opposing
2. an opposed condition; resistance, contradiction, contrast, hostility, etc.
3. 1. any person, group, or thing that opposes
   2. a political party opposing, and serving as a check on, the party in power
4. Astrol., Astron. the position of two celestial bodies when their celestial longitudes differ by 180°; esp., the position of a superior planet or the full moon when it is in opposition with the sun
5. Law the refusal of a creditor to assent to a debtor's release under the bankruptcy law
6. Logic the relation of exclusion or inclusion which exists between propositions having the same subject and predicate but differing in quality, quantity, or both

Etymology: ME opposicioun < OFr opposition < L oppositio < oppositus, pp. of opponere: see opponent