[1] : The Collaborative International Dictionary of English v.0.48

illative \il"lative\, n.
   an illative particle, as for, because.
   1913 webster

[2] : The Collaborative International Dictionary of English v.0.48

illative \il"lative\, a. l. illativus: cf. f. illatif.
   relating to, dependent on, or denoting, illation;
   inferential; conclusive; as, an illative consequence or
   proposition; an illative word, as then, therefore, etc.
   1913 webster

   illative conversion logic, a converse or reverse
      statement of a proposition which in that form must be true
      because the original proposition is true.

   illative sense metaph., the faculty of the mind by which
      it apprehends the conditions and determines upon the
      correctness of inferences.
      1913 webster
see also:
illative conversion illative sense 

[3] : WordNet (r) 2.0

illative
     adj 1: relating to or having the nature of illation or inference;
            "the illative faculty of the mind" syn: inferential
     2: resembling or dependent on or arrived at by inference; "an
        illative conclusion"; "inferential reasoning" syn: inferential
     3: expressing or preceding an inference; "`therefore' is an
        illative word"
see also:
inferential 

Illative >> I Words
Illative, definition of term: Illative
illative_pag1.html