bit part vs soubrette

bit part and soubrette both are nouns.

Word	Noun	Adjective	Verb	Adverb
bit part	Yes	No	No	No
soubrette	Yes	No	No	No

As nouns, soubrette is a hyponym of bit part; that is, soubrette is a word with a more specific, narrower meaning than bit part:

bit part: a small role
soubrette: a minor female role as a pert flirtatious lady's maid in a comedy

bit part (noun)	soubrette (noun)
a small role	a minor female role as a pert flirtatious lady's maid in a comedy
	a pert or flirtatious young girl