en·sure 
(ĕn-shr)
(ĕn-shr)tr.v. en·sured, en·sur·ing, en·sures
To make sure or certain; insure: Our precautions ensured our safety. See Usage Note at assure.
[Middle English ensuren, from Anglo-Norman enseurer : Old French en-, causative pref.; see EN-1 + Old French seur, secure, variant of sur; see SURE.]