antedate

from The American Heritage® Dictionary of the English Language, 5th Edition.

• transitive verb To be of an earlier date than; precede in time.
• transitive verb To assign to a date earlier than that of the actual occurrence.
• transitive verb To date as of a time before that of actual execution.
• noun A date given to an event or a document that is earlier than the actual date.

from The Century Dictionary.

• noun A prior date; a date antecedent to another, or to the true or actual date of a document or event.
• noun Anticipation.
• To date before the true time; give an earlier date to than the real one: thus, to antedate a deed or bond is to give to it a date anterior to the true time of its execution.
• To be of older date than; precede in time.
• To anticipate; realize or give effect to (something) in advance of its actual or proper time.

from the GNU version of the Collaborative International Dictionary of English.

• noun Prior date; a date antecedent to another which is the actual date.
• noun obsolete Anticipation.
• transitive verb To date before the true time; to assign to an earlier date; .
• transitive verb To precede in time.
• transitive verb To anticipate; to make before the true time.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb To occur before an event or time; to exist further back in time
• verb To assign a date to a document or action earlier than the actual date; to backdate

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb be earlier in time; go back further
• verb establish something as being earlier relative to something else