v. a.
1.
Make certain or sure, free from doubt or uncertainty.
2.
Embolden, encourage, enhearten, hearten, make confident.
3.
Declare to ( confidently and earnestly ), vouch to, vow to, protest to, aver to, solemnly promise, pledge, guarantee, warrant.
4.
( Law .) Insure, agree to indemnify for loss, secure against loss.