Asseverate

to declare earnestly or solemnly; affirm positively; aver.
Historical Examples

And I hereby do fully and freely declare and asseverate, that the Woods did not tremble to a kiss, and that the lovers did.
Life of Lord Byron, Vol. 6 (of 6) Thomas Moore

She did not asseverate any more, nor even say she was innocent.
Sue, A Little Heroine L. T. Meade

They lacked a definite opinion to entertain and a cry to asseverate.
In the Name of the Bodleian and Other Essays Augustine Birrell

No one appeared to think it worth while to asseverate the fact, for it was self-evident.
Black Ivory R.M. Ballantyne

They asseverate with vehemence that in all the seven-and-thirty plays there is no such thing as a native woodnote wild.
A Century of Science and Other Essays John Fiske

He could asseverate with some justice, “I have never written an insincere note.”
Musical Portraits Paul Rosenfeld

It has more solemnity than declare, and more composure and dignity than asseverate, which is to assert excitedly.
English Synonyms and Antonyms James Champlin Fernald

“Wh-why, nobudy ever heard me talkin’ things that’s tol’ in secret,” Mike made haste to asseverate.
The Lookout Man B. M. Bower

As to whether she was young, middle-aged or only well-preserved, no one was in a position to asseverate.
Anderson Crow, Detective George Barr McCutcheon

And she was very glad also that he did not deign to asseverate that he had been ignorant of his half-sister’s plight.
Hilda Lessways Arnold Bennett

verb
(transitive) to assert or declare emphatically or solemnly
v.

1791, from Latin asseveratus, past participle of asseverare “to affirm, insist on, maintain,” from ad- “to” (see ad-) + severus “serious, severe” (see severe). Related: Asseverated; asseverating.