Ensure/ɪnˈʃʊr/ Definition 1 of 3Pro Tip 1/3Action Required Use 'ensure' when an action must be taken to guarantee an outcome. Ensure you study daily to improve your English. Pro Tip 2/3Future Certainty 'Ensure' often relates to something that will happen in the future. Ensure your passport is valid for your trip next month. Pro Tip 3/3Personal Responsibility Indicates personal obligation to make something happen. You must ensure you are on time for the meeting.