c.1600, from Latin intensionem (nominative intensio) "a stretching, straining, effort," noun of action from past participle stem of intendere (see intend).
in logic, correlative words that indicate the reference of a term or concept: "intension" indicates the internal content of a term or concept that constitutes its formal definition; and "extension" indicates its range of applicability by naming the particular objects that it denotes. For instance, the intension of "ship" as a substantive is "vehicle for conveyance on water," whereas its extension embraces such things as cargo ships, passenger ships, battleships, and sailing ships. The distinction between intension and extension is not the same as that between connotation and denotation.