The Collaborative International Dictionary of English v.0.48:

Antedate \An"te*date`\ ([a^]n`t[-e]*d[=a]t`), n.
   1. Prior date; a date antecedent to another which is the
      actual date.
      [1913 Webster]

   2. Anticipation. [Obs.] --Donne.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Antedate \An"te*date`\ ([a^]n`t[-e]*d[=a]t`), v. t. [imp. & p.
   p. Antedated; p. pr. & vb. n. Antedating.]
   1. To date before the true time; to assign to an earlier
      date;; thus, to antedate a deed or a bond is to give it a
      date anterior to the true time of its execution.
      [1913 Webster]

   2. To precede in time.
      [1913 Webster]

   3. To anticipate; to make before the true time.
      [1913 Webster]

            And antedate the bliss above.         --Pope.
      [1913 Webster]

            Who rather rose the day to antedate.  --Wordsworth.
      [1913 Webster]

WordNet (r) 3.0 (2006):

antedate
    v 1: be earlier in time; go back further; "Stone tools precede
         bronze tools" [syn: predate, precede, forego,
         forgo, antecede, antedate] [ant: follow,
         postdate]
    2: establish something as being earlier relative to something
       else [syn: predate, antedate, foredate] [ant:
       postdate]