intension and extension, 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.Encyclopaedia Britannica, “intension and extension”
Pair of terms associated with J. S. Mill, and marking much the same distinction as the currently more usual intension/extension. The denotation of a singular term is the object to which it refers, and of a predicate the set of objects satisfying it. The connotation is the abstract meaning, or principle or condition whereby something is picked out as denoted by the term.The Oxford Dictionary of Philosophy, “connotation/denotation”
While the Britannica entry is claiming to be about logic and the Oxford is about the Millian terms connotation and denotation, it still is confusing as to what the difference is between Mill’s logic and non-Mill’s logic, if indeed this is the point of difference.
Either way, we have varying definitions, which, ironically, is at the heart of the very problem of these terms — meaning.