polar star vs Polaris

polar star and Polaris both are nouns.

Word	Noun	Adjective	Verb	Adverb
polar star	Yes	No	No	No
Polaris	Yes	No	No	No

As nouns, polar star and Polaris are synonyms defined as:

polar star and Polaris: the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it

Other synonyms of polar star include North Star, pole star, polestar.

polar star (noun)	Polaris (noun)
the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it	the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it