Professional means done as a paid job rather than as a pastime. A professional musician, turn professional, professional standards.
The word does two jobs: paid rather than amateur, and behaving with proper standards, so calling somebody unprofessional says nothing about their pay. In sport, turning professional is a formal step that ends amateur eligibility.
1adjectiveprofessionalDone as a paid job rather than as a pastime.
“After years of playing for fun, she became a professional tennis player at nineteen.”
professional is a quality.
From profession, from Latin professio, a public declaration, from profiteri, to declare openly.
Middle English
professhennalle
English, today
professional
From Middle English professhennalle, professhynalle; equivalent to profession + al.
Etymology from Wiktionary, CC BY-SA