Meaning

verb establish or strengthen as with new evidence or facts

verb to declare or affirm solemnly and formally as true

verb say yes to

originFrom Middle English affermen, from Old French afermer, affermer, from Latin affirmare, adfirmare (“to present as fixed, aver, affirm”), from ad (“to”) + firmare (“to make firm”), from firmus (“firm”). By surface analysis, af- + firm.

Etymology from Wiktionary, CC BY-SA 3.0