bilingualist vs polyglot

bilingualist and polyglot both are nouns.

Word	Noun	Adjective	Verb	Adverb
bilingualist	Yes	No	No	No
polyglot	Yes	Yes	No	No

As nouns, polyglot is a hypernym of bilingualist; that is, polyglot is a word with a broader meaning than bilingualist:

Other hypernyms of bilingualist include linguist.

bilingualist (noun)	polyglot (noun)
a person who speaks two languages fluently	a person who speaks more than one language

bilingualist (adjective)	polyglot (adjective)
	having a command of or composed in many languages