star vs co-star

star and co-star both are nouns.

Word	Noun	Adjective	Verb	Adverb
star	Yes	Yes	Yes	No
co-star	Yes	No	Yes	No

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

star: an actor who plays a principal role
co-star: one of two actors who are given equal status as stars in a play or film

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

As verbs, co-star is a hyponym of star; that is, co-star is a word with a more specific, narrower meaning than star:

As verbs, co-star is a hyponym of star; that is, co-star is a word with a more specific, narrower meaning than star:

star (noun)	co-star (noun)
the topology of a network whose components are connected to a hub	one of two actors who are given equal status as stars in a play or film
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)	co-star (adjective)
indicating the most important performer or role

star (verb)	co-star (verb)
mark with an asterisk	be the co-star in a performance
be the star in a performance	feature as the co-star in a performance
feature as the star