1 secure, stabilize, settle, establish, confirm, certify, warrant, guarantee, ensure, be confident of, make or be sure or certain:
Force, fear, and the multitude of his guard do less to assure the estate of a prince than the good will of his subjects.
2 encourage, inspirit, reassure, hearten:
Your humanity assures us and gives us strength.
3 convince, persuade, reassure, make (someone) certain; ensure:
What can I do to assure you of my love?
4 assert, state, asseverate, promise:
I assure you that we shall do everything possible to find your dog.