'backdate' definitions:

Definition of 'backdate'

(from WordNet)
verb
Make effective from an earlier date; "The increase in tax was backdated to January"

Definition of 'backdate'

From: GCIDE
  • backdate \back"date\ v. t.
  • 1. to make effective from an earlier date; to make retroactive. The increase in tax was backdated to January.
  • Syn: back-date [WordNet 1.5]
  • 2. to affix a date earlier than the present date; -- sometimes done for fraudulent purposes. Opposite of postdate.
  • Syn: back-date; predate; antedate. [PJC]
  • Note: Backdate is sometimes used incorrectly for postdate.