assure

make certain of; "This nest egg will ensure a nice retirement for us"; "Preparation will guarantee success!"

inform positively and with certainty and confidence; "I tell you that man is a crook!"

assure somebody of the truth of something with the intention of giving the listener confidence; "I assured him that traveling to Cambodia was safe"

be careful or certain to do something; make certain of something; "He verified that the valves were closed"; "See that the curtains are closed"; "control the quality of the product"

cause to feel sure; give reassurance to; "The airline tried to reassure the customers that the planes were safe"

make a promise or commitment