professional has 3 distinct synonyms spread across 3 of its 8 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its 3 recorded opposites are nonprofessional, unprofessional, amateur.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
engaged in a profession or engaging in as a profession or means of livelihood
“the professional man or woman possesses distinctive qualifications”
characteristic of or befitting a profession or one engaged in a profession
“professional conduct”
a person engaged in one of the learned professions
an athlete who plays for pay
3 of the 8 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for professional.
Synonyms, antonyms and the broader and narrower relations for professional come from Princeton University’s WordNet. Full sources and licences.