ensure

(verb) make certain of. Synonyms: guarantee, insure, assure, secure. Examples: "This nest egg will ensure a nice retirement for us." "Preparation will guarantee success!."

(verb) be careful or certain to do something; make certain of something. Synonyms: see, check, insure, see to it, control, ascertain, assure. Examples: "He verified that the valves were closed." "See that the curtains are closed." "Control the quality of the product."