backdate

• POS: Verb (transitive)
• HYPHEN: back=date

CIDE DICTIONARY

backdate, v. t. 

•  to make effective from an earlier date; to make retroactive.  [WordNet 1.5]
•  to affix a date earlier than the present date; -- sometimes done for fraudulent purposes. Opposite of postdate.  [PJC]

  "Backdate is sometimes used incorrectly for postdate."

OXFORD DICTIONARY

backdate, v.tr.
1 put an earlier date to (an agreement etc.) than the actual one.
2 make retrospectively valid.

ROGET THESAURUS

backdate

Anachronism

VB misdate, antedate, postdate, backdate, overdate, anticipate, take no note of time, lose track of time, anachronize.