The Collaborative International Dictionary of English v.0.48:

Demonstrative \De*mon"stra*tive\, n. (Gram.)
   A demonstrative pronoun; as, "this" and "that" are
   demonstratives.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            An argument necessary and demonstrative. --Hooker.
      [1913 Webster]

   2. Expressing, or apt to express, much; displaying feeling or
      sentiment; as, her nature was demonstrative.
      [1913 Webster]

   3. Consisting of eulogy or of invective. "Demonstrative
      eloquence." --Blair.
      [1913 Webster]

   Demonstrative pronoun (Gram.), a pronoun distinctly
      designating that to which it refers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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: demonstrative, illustrative]
    n 1: a pronoun that points out an intended referent [syn:
         demonstrative pronoun, demonstrative]