polestar vs pole star

polestar and pole star both are nouns.

Word	Noun	Adjective	Verb	Adverb
polestar	Yes	No	No	No
pole star	Yes	No	No	No

As nouns, polestar and pole star are synonyms defined as:

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

polestar (noun)	pole 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