star vs TV star

star and TV star both are nouns.

Word	Noun	Adjective	Verb	Adverb
star	Yes	Yes	Yes	No
TV star	Yes	No	No	No

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

Other hyponyms of star include co-star, film star, movie star, idol, matinee idol, television star.

star (noun)	TV star (noun)
the topology of a network whose components are connected to a hub	a star in a television show
a star-shaped character * used in printing
(astronomy) a celestial body of hot gases that radiates energy derived from thermonuclear reactions in the interior
any celestial body visible (as a point of light) from the Earth at night
an actor who plays a principal role
someone who is dazzlingly skilled in any field
a performer who receives prominent billing
a plane figure with 5 or more points; often used as an emblem

star (adjective)	TV star (adjective)
indicating the most important performer or role