Assure, v. t. [imp. & p. p. Assured; p. pr. & vb. n. Assuring.]
Etymology: [OF. aseürer, F. assurer, LL. assecurare; L. ad + securus secure, sure, certain. See Secure, Sure, and cf. Insure.]
1. To make sure or certain; to render confident by a promise, declaration, or other evidence. His promise that thy seed shall bruise our foe . . . Assures me that the bitterness of death Is past, and we shall live. Milton.
2. To declare to, solemnly; to assert to (any one) with the design of inspiring belief or confidence. I dare assure thee that no enemy Shall ever take alive the noble Brutus. Shak.
3. To confirm; to make certain or secure. And it shall be assured to him. Lev. xxvii. 19. And hereby we know that we are of the truth, and shall assure our hearts before him. 1 John iii. 19.
4. To affiance; to betroth. [Obs.] Shak.
3 more senses
5. (Law)
To insure; to covenant to indemnify for loss, or to pay a specified sum at death. See Insure.
Syn. -- To declare; aver; avouch; vouch; assert; asseverate; protest; persuade; convince.
Shades of meaning
Fernald has no entry of its own for assure; he lists it under confirm, state.
Where he writes about it:
To assure is to state with such authority and confidence as the speaker feels ought to make the hearer sure. — from state
Assure, certify, inform, apply to the person; affirm, etc., to the thing. — from state
Assert is combative; assure is conciliatory. — from state
I assert my right to cross the river; I assure my friend it is perfectly safe. — from state