'profess' originates from Old French, specifically the word 'professer', which itself derives from Latin 'professari' (frequentative of 'profitēri'/'profiteri'), where 'pro-' meant 'forth' and 'fateri' (or the related root) meant 'to speak' or 'to confess'.

'profess' changed from the Middle English word 'professen' (borrowed via Old French 'professer') and eventually became the modern English word 'profess'.

Initially, it meant 'to make a public declaration' or 'to take vows' (as in religious professions); over time it broadened to mean 'to declare or claim (sometimes without proof)' and 'to declare belief in' in modern usage.