assure

make certain of

This nest egg will ensure a nice retirement for us

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

cause to feel sure; give reassurance to

The airline tried to reassure the customers that the planes were safe