'avow' originates from Old French, specifically the word 'avouer', where the root meant 'to acknowledge, confess'.

'avow' changed from Old French 'avouer' (acknowledge, confess) and Middle English 'avowen' and eventually became the modern English word 'avow'.

Initially it meant 'to acknowledge or confess', and over time it has largely retained that meaning while broadening to include any open declaration or assertion.