Source : Webster's Revised Unabridged Dictionary (1913)

Expostulate \Ex*pos"tu*late\, v. t.
   To discuss; to examine. [Obs.]

         To expostulate What majesty should be, what duty is.
                                                  --Shak.

Expostulate \Ex*pos"tu*late\ (?; 135), v. i. [imp. & p. p.
   {Expostulated}; p. pr. & vb. n. {Expostulating}.] [L.
   expostulatus, p. p. of expostulare to demand vehemently; ex
   out + postulare to ask, require. See {Postulate}.]
   To reason earnestly with a person on some impropriety of his
   conduct, representing the wrong he has done or intends, and
   urging him to make redress or to desist; to remonstrate; --
   followed by with.

         Men expostulate with erring friends; they bring
         accusations against enemies who have done them a wrong.
                                                  --Jowett
                                                  (Thuc. ).

   Syn: To remonstrate; reason. See {Remonstrate}.

Source : WordNet®

expostulate
     v : reason with (somebody) for the purpose of dissuasion