Source : Webster's Revised Unabridged Dictionary (1913)

Extensional \Ex*ten"sion*al\, a.
   Having great extent.

Source : WordNet®

extensional
     adj : used of the class of entities to which a given word
           correctly applies

Source : Free On-Line Dictionary of Computing

extensional
     
        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.