What does antedate mean?
The definition of antedate
An”te*date`, n.
1 Prior date; a date antecedent to another which is the actual date.
2 Anticipation. [Obs.] Donne.
An”te*date`, 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.
2 To precede in time.
3 To anticipate; to make before the true time. And antedate the bliss above. Pope. Who rather rose the day to antedate. Wordsworth.