Axiom:Axiom of Extension/Linguistic Note

Linguistic Note on
The nature of the ', or ' as it is frequently called, suggests that the Axiom of Extent, ought in fact to be the preferred name, as it gives a precise definition of the extent of a collection.

However, the word extensionality is a term in logic which determines equality of objects by its external features, as opposed to intensionality, which is more concerned with internal structure.