binary star vs double star

binary star and double star both are nouns.

Word	Noun	Adjective	Verb	Adverb
binary star	Yes	No	No	No
double star	Yes	No	No	No

As nouns, binary star and double star are synonyms defined as:

binary star and double star: a system of two stars that revolve around each other under their mutual gravitation

Other synonyms of binary star include binary.

binary star (noun)	double star (noun)
a system of two stars that revolve around each other under their mutual gravitation	a system of two stars that revolve around each other under their mutual gravitation