ensure definition : make certain something happens or is the case. Check meanings, examples, usage tips, pronunciation, domains, related words. ensure --verb (verb: ensure ;3rd person present:ensures;past tense:ensured;past participle:ensured;gerund or present participle:ensuring) 1. to make certain of "This nest egg will ensure a nice retirement for us." Ensure definition : to secure or guarantee.. See examples of ENSURE used in a sentence. Master the word " ENSURE " in English: definitions, translations, synonyms, pronunciations, examples, and grammar insights - all in one complete resource.