(semantics) A definition of a term that specifies its extension, that is, every object that falls under the definition.

Of or pertaining to extension. / Having great extent.

(computing) Lacking a file extension.

In terms or by means of extension.

(set theory) One of the axioms in axiomatic set theory, equivalent to the statement that two sets are equal if and only if they contain the same elements.

(philosophy) The principle that objects are equal if and only if their observed properties are the same, regardless of internal processes that lead to those properties.

plural of extensionist

One who favours or advocates extension.

plural of extensionality

(philosophy) The belief in extensionality.