ballet mistress vs dancer

ballet mistress and dancer both are nouns.

Word	Noun	Adjective	Verb	Adverb
ballet mistress	Yes	No	No	No
dancer	Yes	No	No	No

As nouns, dancer is a hypernym of ballet mistress; that is, dancer is a word with a broader meaning than ballet mistress:

ballet mistress: a woman who directs and teaches and rehearses dancers for a ballet company
dancer: a performer who dances professionally

Other hypernyms of ballet mistress include professional dancer, terpsichorean.

ballet mistress (noun)	dancer (noun)
a woman who directs and teaches and rehearses dancers for a ballet company	a performer who dances professionally
	a person who participates in a social gathering arranged for dancing (as a ball)