extension (n.)

A term in philosophy and logic, and now often used as part of a theoretical framework for LINGUISTIC SEMANTICS, to refer to the entity or class of entities to which a WORD is correctly applied. For example, the extension (or extensional meaning) of the term flower would be the set of all flowers. ‘Extension’ is the REFERENT or DENOTATION of a word, as opposed to its INTENSION, which includes only the defining properties of terms. For ‘extensional contexts’.

In HISTORICAL LINGUISTICS, extension is used in the classification of types of SEMANTIC change, referring to a widening of meaning in a LEXICAL item; opposed to NARROWING. For example, in Latin ‘virtue’ was a male quality (cf. vir ‘man’), but today it applies to both sexes.