theater vs co-star

theater and co-star both are nouns.

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

theater (noun)	co-star (noun)
a building where theatrical performances or motion-picture shows can be presented	one of two actors who are given equal status as stars in a play or film
the art of writing and producing plays
a region in which active military operations are in progress

theater (verb)	co-star (verb)
	be the co-star in a performance
	feature as the co-star in a performance