Antedate Definition: To date back; retroactively. Related Terms: Nunc Pro Tunc To date a document to a time before it was actually written or signed.In patent law, a strategy of some limited protection involves preparing an affidavit on an early date in an effort to antedate the application of any interfering application for a patent on the same subject matter. Categories & Topics: Contract Law Dictionary Find you are constantly looking up definitions? Try our search provider (works in most modern browsers) If you find an error or omission in Duhaime's Legal Dictionary, or if you have legal term suggestion, we'd love to hear from you!