'profess' originates from Latin, specifically the word 'profitēri' (also seen as 'profiteri'), where the prefix 'pro-' meant 'forth' and the root related to Latin 'fāri/fateri' meant 'to speak/confess'.

'profess' passed into Old French as 'professer' and Middle English as 'professen', eventually becoming modern English 'profess' with past/p.p. 'professed'.

Initially it meant 'to declare openly or confess', and over time it retained that sense while also developing related meanings such as 'to claim (sometimes falsely)' and 'to hold or teach a profession or belief'.