bit part vs theatrical role

bit part and theatrical role both are nouns.

Word	Noun	Adjective	Verb	Adverb
bit part	Yes	No	No	No
theatrical role	Yes	No	No	No

As nouns, theatrical role is a hypernym of bit part; that is, theatrical role is a word with a broader meaning than bit part:

Other hypernyms of bit part include character, part, persona, role.

bit part (noun)	theatrical role (noun)
a small role	an actor's portrayal of someone in a play