Available Definitions:
1) a. - Of or pertaining to a profession, or calling; conforming to the rules or standards of a profession; following a profession; as, professional knowledge; professional conduct.
2) a. - Engaged in by professionals; as, a professional race; -- opposed to amateur.
3) n. - A person who prosecutes anything professionally, or for a livelihood, and not in the character of an amateur; a professional worker.