character vs bit part

character and bit part both are nouns.

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

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

Other hyponyms of character include minor role, heavy, hero, ingenue, name part, title role, heroine, baddie, villain.

character (noun)	bit part (noun)
(genetics) an attribute (structural or functional) that is determined by a gene or group of genes	a small role
the inherent complex of attributes that determines a persons moral and ethical actions and reactions
a characteristic property that defines the apparent individual nature of something
an actor's portrayal of someone in a play
a written symbol that is used to represent speech
a formal recommendation by a former employer to a potential future employer describing the person's qualifications and dependability
a person of a specified kind (usually with many eccentricities)
an imaginary person represented in a work of fiction (play or film or story)
good repute

character (verb)	bit part (verb)
engrave or inscribe characters on