In lexical semantics, opposites are words lying in an inherently incompatible binary relationship. For example, something that is even entails that it is not odd. It is referred to as a 'binary' relationship because there are two members in a set of opposites. The relationship between opposites is known as opposition. A member of a pair of opposites can generally be determined by the question: "What is the opposite of X"

The term antonym (and the related antonymy)