polar star vs North Star

polar star and North Star both are nouns.

Word	Noun	Adjective	Verb	Adverb
polar star	Yes	No	No	No
North Star	Yes	No	No	No

As nouns, polar star and North Star are synonyms defined as:

polar star and North Star: 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 Polaris, pole star, polestar.

polar star (noun)	North Star (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