star sign vs sign of the zodiac

star sign and sign of the zodiac both are nouns.

Word	Noun	Adjective	Verb	Adverb
star sign	Yes	No	No	No
sign of the zodiac	Yes	No	No	No

As nouns, star sign and sign of the zodiac are synonyms defined as:

star sign and sign of the zodiac: (astrology) one of 12 equal areas into which the zodiac is divided

Other synonyms of star sign include house, mansion, planetary house, sign.

star sign (noun)	sign of the zodiac (noun)
(astrology) one of 12 equal areas into which the zodiac is divided	(astrology) one of 12 equal areas into which the zodiac is divided