comedian vs top banana

comedian and top banana both are nouns.

Word	Noun	Adjective	Verb	Adverb
comedian	Yes	No	No	No
top banana	Yes	No	No	No

As nouns, top banana is a hyponym of comedian; that is, top banana is a word with a more specific, narrower meaning than comedian:

comedian: a professional performer who tells jokes and performs comical acts
top banana: the leading comedian in a burlesque show

Other hyponyms of comedian include buffoon, clown, goof, goofball, merry andrew, comedienne, gagman, standup comedian, joker, jokester.

comedian (noun)	top banana (noun)
a professional performer who tells jokes and performs comical acts	the leading comedian in a burlesque show
an actor in a comedy	the most important person in a group or undertaking