extensional

In Philosophy of language, a context in which a subsentential expression e appears is called extensional if and only if e can be replaced by an expression with the same extension and necessarily preserve truth-value. The extension of a term is the set of objects that that term denotes.Take the case of Clark Kent, who is Superman. Suppose that Lois Lane fell out of a window and Superman caught her. Thus the statement, "Clark Kent caught Lois Lane," is true because it has an extensional context. The names "Superman" and "Clark Kent" have the same extension, which is to say that they both refer to the same person, i.e. that superhero who is vulnerable to kryptonite. Anybody that Superman caught, Clark Kent caught.
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(a.)
Having great extent.
  

Extensional properties, e.g. extensional equality, relate to the "black-box" behaviour of an object, i.e. how its output depends on its input. The opposite is intensional which concerns how the object is implemented.

Adjective
1. used of the class of entities to which a given word correctly applies
(similar) denotative, denotive
(classification) logic