noun

• The action of opposing or of being in conflict.
• An opposite or contrasting position.
• (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.
• (politics) A political party or movement opposed to the party or government in power.
• (law) In United States intellectual property law, a proceeding in which an interested party seeks to prevent the registration of a trademark or patent.
• (chess) A position in which the player on the move must yield with his king allowing his opponent to advance with his own king.
• (logic) The difference of quantity or quality between two propositions having the same subject and predicate.