oppositional

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