To antedate is to assign a date to a contract, check, or IOU that precedes the execution date of the document. For example:
The date of a check is stated as being prior to the date on which the check was actually written.
A contract may be deliberately antedated to provide a beneficiary a greater benefit than should really be the case. For example, a stock option agreement can be antedated in order to set the initial stock option price at a lower market price that existed in the past. There can also be legitimate reasons for antedating a contract. For example, the execution of a contract has been delayed due to circumstances beyond the control of the participants, so the contract is antedated back to the date when it would normally have been executed.