To confirm or ratify; to declare positively or solemnly.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (verb) (v.) (verb)
To assert strongly; to confirm, as a judgment, decree, or order, in court.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (verb) (v. t.) (verb transitive)
To assert with confidence; to maintain confidently as true; to declare solemnly.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (verb) (v.) (verb)
To assert confidently or positively.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (verb) (v. t.) (verb transitive)
To declare positively.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (verb) (v.) (verb)

Usage examples:

We affirm the divine supply.
- Modern Religious Cults and Movements by Gaius Glenn Atkins
" I affirm then, that you leave many enemies behind you here to go yonder and bring more back with you.
- The History of the Peloponnesian War by Thucydides
Here, however, we would not take it upon us to affirm any thing in respect of the motives which influenced the obedience.
- A General History and Collection of Voyages and Travels, Volume 16 by Robert Kerr