rocker vs rock star

rocker and rock star both are nouns.

Word	Noun	Adjective	Verb	Adverb
rocker	Yes	No	No	No
rock star	Yes	No	No	No

As nouns, rock star is a hyponym of rocker; that is, rock star is a word with a more specific, narrower meaning than rocker:

rocker (noun)	rock star (noun)
a curved support that permits the supported object to rock to and fro	a famous singer of rock music
a chair mounted on rockers
an ice skate with a curved blade
a trough that can be rocked back and forth; used by gold miners to shake auriferous earth in water in order to separate the gold
a teenager or young adult in the 1960s who wore leather jackets and rode motorcycles
a performer or composer or fan of rock music
an attendant who rocks a child in a cradle