Source : Webster's Revised Unabridged Dictionary (1913)

Demonstrative \De*mon"stra*tive\, a. [F. d['e]monstratif, L.
   demonstrativus.]
   1. Having the nature of demonstration; tending to
      demonstrate; making evident; exhibiting clearly or
      conclusively. ``Demonstrative figures.'' --Dryden.

            An argument necessary and demonstrative. --Hooker.

   2. Expressing, or apt to express, much; displaying feeling or
      sentiment; as, her nature was demonstrative.

   3. Consisting of eulogy or of invective. ``Demonstrative
      eloquence.'' --Blair.

   {Demonstrative pronoun} (Gram.), a pronoun distinctly
      designating that to which it refers.

Demonstrative \De*mon"stra*tive\, n. (Gram.)
   A demonstrative pronoun; as, ``this'' and ``that'' are
   demonstratives.

Source : WordNet®

demonstrative
     adj 1: given to or marked by the open expression of emotion; "an
            affectionate and demonstrative family" [ant: {undemonstrative}]
     2: serving to demonstrate [syn: {illustrative}]

demonstrative
     n : a pronoun that points out an intended referent [syn: {demonstrative
         pronoun}]