Brief etymology of "professor": From Latin "profiteri", to the form "profess-" meaning "declared publicly", and to "professor", then to Late Middle English as

Brief etymology of "professor": From Latin "profiteri", to the form "profess-" meaning "declared publicly", and to "professor", then to Late Middle English as "professor". So a professor's practice is probably closer to definition 2: "make a public declaration of" whatever one's skill or knowledge of a particular art might be.