opposition

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act of opposing or resisting.
• noun The condition of being in conflict; antagonism.
• noun Placement opposite to or in contrast with another.
• noun Something that serves as an obstacle.
• noun A political party or an organized group opposed to the group, party, or government in power.
• noun The position of two celestial bodies when their longitude differs by 180°, especially a configuration in which Earth lies on a straight line between the sun and a superior planet or the moon.
• noun The position of the superior planet or the moon in this configuration.
• noun Logic The relation existing between two propositions having an identical subject and predicate but differing in quantity, quality, or both.
• noun Linguistics Contrast in a language between two phonemes or other linguistically important elements.

from The Century Dictionary.

• noun In astrology, the aspect formed between two heavenly bodies 180 degrees (or about that distance) from each other: regarded as inimical and pernicious.
• noun The position of that which confronts, faces, or stands over against something else.
• noun In astronomy, the situation of two heavenly bodies when diametrically opposed to each other as seen from the earth's surface, or when their longitudes differ by 180°.
• noun The action of opposing, withstanding, resisting, or checking; antagonism; encounter.
• noun A placing opposite, as for purposes of comparison, contrast, etc., or the state of being so placed, opposed, or contrasted; contrariety.
• noun In logic, the disagreement between propositions which have the same subject or the same predicate, but differ in quantity or quality, or in both; also, the relation between two terms which are contrasted in any respect.
• noun In the fine arts, contrast.
• noun A body of opposers; specifically, those members of a legislative body who are opposed to the administration for the time being, or the political party opposed to the party in power: frequently used adjectively: as, an opposition scheme; the opposition benches in the British House of Commons.
• noun In fencing. See the quotation.
• noun In chess, a position where the king of the player who has not the move is directly in front of that of his opponent with one vacant square between.
• noun See the adjectives.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of opposing; an attempt to check, restrain, or defeat; resistance.
• noun The state of being placed over against; situation so as to front something else.
• noun Repugnance; contrariety of sentiment, interest, or purpose; antipathy.
• noun That which opposes; an obstacle; specifically, the aggregate of persons or things opposing; hence, in politics and parliamentary practice, the party opposed to the party in power.
• noun (Astron.) The situation of a heavenly body with respect to another when in the part of the heavens directly opposite to it; especially, the position of a planet or satellite when its longitude differs from that of the sun 180°; -- signified by the symbol �.
• noun (Logic) The relation between two propositions when, having the same subject and predicate, they differ in quantity, or in quality, or in both; or between two propositions which have the same matter but a different form.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The action of opposing or of being in conflict.
• noun An opposite or contrasting position.
• noun An opponent in some form of competition.
• noun astronomy The apparent relative position of two celestial bodies when one is at an angle of 180 degrees from the other as seen from the Earth.
• noun politics A political party opposed to the party or government in power.
• noun law In United States intellectual property law, a proceeding in which an interested party seeks to prevent the registration of a trademark or patent.
• noun chess A position in which the player on the move must yield with his king allowing his opponent to advance with his own king.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the major political party opposed to the party in office and prepared to replace it if elected
• noun the relation between opposed entities
• noun a contestant that you are matched against
• noun a body of people united in opposing something
• noun the act of hostile groups opposing each other
• noun a direction opposite to another
• noun an armed adversary (especially a member of an opposing military force)
• noun the action of opposing something that you disapprove or disagree with