Definition of "professional"

professional

/pɹəˈfɛʃənəl/

noun
plural professionals
1. A person who belongs to a profession.
2. A person who earns their living from a specified activity.
3. (euphemistic) A prostitute.
4. A reputation known by name.
5. An expert.
  Quotations
  I have learned that there is a person attached to a golf club called a professional. Find out who fills that post at the Green Meadow Club; […] invite the professional, urgently, to dine with us this evening.
  1934, Rex Stout, Fer-de-Lance, Bantam, published 1992, page 97
6. One of four categories of sociologist propounded by Horowitz: a sociologist who is actively concerned with promoting the profession of sociology.
adjective
comparative more professional, superlative most professional
1. Of, pertaining to, or in accordance with the (usually high) standards of a profession.
  Quotations
  His forefathers had been, as a rule, professional men—physicians and lawyers; his grandfather died under the walls of Chapultepec Castle while twisting a tourniquet for a cursing dragoon; an uncle remained indefinitely at Malvern Hill; […].
  1907 August, Robert W[illiam] Chambers, chapter II, in The Younger Set, New York, N.Y.: D. Appleton & Company
  The little green men were clearly professional soldiers by their bearing, carried Russian weapons, and wore Russian combat fatigues, but they had no identifying insignia. Vladimir Putin originally denied they were Russian soldiers; that April, he confirmed they were.
  2019 March 18, Steven Pifer, Five years after Crimea’s illegal annexation, the issue is no closer to resolution‎, The Center for International Security and Cooperation
2. That is carried out for money, especially as a livelihood.
3. (by extension) Expert.