Lewis & Short

af-firmo (better adf-), āvi, ātum, 1, v. a.

  1. I. To present a thing in words, as fixed, firm, i. e. certain, true; to assert, maintain, aver, declare, asseverate, affirm: dicendum est mihi, sed ita, nihil ut adfirmem, quaeram omnia, Cic. Div. 2, 3; so id. Att. 13, 23; id. Brut. 1, 1: jure jurando, Liv. 29, 23: quidam plures Deo ortos adfirmant, Tac. G. 2; cf. id. Agr. 10: adfirmavit non daturum se, he protested that he would give nothing, Suet. Aug. 42.
    Impers.: atque affirmatur, Tac. H. 2, 49.
    Hence,
  2. II. To give confirmation of the truth of a thing, to strengthen, to confirm, corroborate, sanction: adfirmare spem alicui, Liv. 1, 1: opinionem, id. 32, 35: dicta alicujus, id. 28, 2: aliquid auctoritate sua, id. 26, 24: populi Romani virtutem armis, Tac. H. 4, 73: secuta anceps valetudo iram Deūm adfirmavit, id. A. 14, 22.
    Hence, * affirmanter (adf-), adv. (of the absol. P. a. affirmans), with assurance or certainty, assuredly: praedicere aliquid, Gell. 14, 1, 24; and: af-firmātē (adf-), adv. (of the absol. P. a. affirmatus), with asseveration, with assurance, certainly, assuredly, positively: quod adfirmate, quasi Deo teste promiserit, id tenendum est, Cic. Off. 3, 29.
    Sup.: adfirmatissime scribere aliquid, Gell. 10, 12, 9.