Annul/əˈnʌl/ Definition 1 of 3Pro Tip 1/3Legal Endings Annul is often used to describe the legal end of agreements, as if they never existed. They moved to annul the lease agreement. Pro Tip 2/3Irreversible Process 'Annul' usually implies a final, irreversible action, with no chance to revert it. Once their marriage was annulled, it was as if it never happened. Pro Tip 3/3Not for Errors Use 'annul' for formal cancellations, not for correcting everyday mistakes. The company cannot simply annul an order because of a pricing mistake.