(1) To date something (such as a check) with a date earlier than that of actual writing. (2) To precede in time.
Example:
Nantucket Island has hundreds of beautifully preserved houses that antedate the Civil War.
Antedate is used when talking about things that can be given dates. Dinosaurs antedated the first human beings by about 65 million years, though this stubborn fact has never stopped cartoonists and moviemakers from having the two species inhabit the same story line. The oral use of a word often antedates its appearance in print by a number of years.