Source : Webster's Revised Unabridged Dictionary (1913)

Postdate \Post"date`\, v. t. [imp. & p. p. {Postdated}; p. pr. &
   vb. n. {Postdating}.] [Pref. post- + date.]
   1. To date after the real time; as, to postdate a contract,
      that is, to date it later than the time when it was in
      fact made.

   2. To affix a date to after the event.

Postdate \Post"date`\, a.
   Made or done after the date assigned.

         Of these [predictions] some were postdate; cunningly
         made after the thing came to pass.       --Fuller.

Postdate \Post"date`\, n.
   A date put to a bill of exchange or other paper, later than
   that when it was actually made.

Source : WordNet®

postdate
     v 1: be later in time; "Tuesday always follows Monday" [syn: {follow}]
          [ant: {predate}]
     2: establish something as being later relative to something
        else [ant: {predate}]