1.make certain of;
This nest egg will ensure a nice retirement for us
2.inform positively and with certainty and confidence;
I tell you that man is a crook!
3.assure somebody of the truth of something with the intention of giving the listener confidence;
I assured him that traveling to Cambodia was safe
4.be careful or certain to do something; make certain of something;
He verified that the valves were closed
5.cause to feel sure; give reassurance to;
The airline tried to reassure the customers that the planes were safe
6.make a promise or commitment