'Professor' originally meant 'one who declares publicly' — not a teacher, but a public declarer of knowledge.
A senior academic holding the highest rank in a university department; more broadly, a person who professes expertise and teaches at a university.
From Latin 'professor' (a person who declares publicly, a teacher), agent noun from 'profiteri' (to declare publicly, to profess), from 'pro-' (before, in front of) + 'fateri' (to acknowledge, to confess). The original sense was not about teaching but about public declaration — a professor was one who openly declared allegiance to a religion, a set of beliefs, or a body of knowledge. The narrowing to an academic title occurred in medieval universities