professional dancer vs dancer

professional dancer and dancer both are nouns.

Word	Noun	Adjective	Verb	Adverb
professional dancer	Yes	No	No	No
dancer	Yes	No	No	No

As nouns, professional dancer and dancer are synonyms defined as:

Other synonyms of professional dancer include terpsichorean.

professional dancer (noun)	dancer (noun)
a performer who dances professionally	a performer who dances professionally
	a person who participates in a social gathering arranged for dancing (as a ball)