red giant star vs red giant

red giant star and red giant both are nouns.

Word	Noun	Adjective	Verb	Adverb
red giant star	Yes	No	No	No
red giant	Yes	No	No	No

As nouns, red giant star and red giant are synonyms defined as:

red giant star and red giant: a large, old, luminous star; has a relatively low surface temperature and a diameter large relative to the sun

red giant star (noun)	red giant (noun)
a large, old, luminous star; has a relatively low surface temperature and a diameter large relative to the sun	a large, old, luminous star; has a relatively low surface temperature and a diameter large relative to the sun