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
make a promise or commitment
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!
cause to feel sure; give reassurance to
The airline tried to reassure the customers that the planes were safe