bigwig vs top banana

bigwig and top banana both are nouns.

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

As nouns, bigwig and top banana are synonyms defined as:

bigwig and top banana: the most important person in a group or undertaking

Other synonyms of bigwig include kingpin.

bigwig (noun)	top banana (noun)
the most important person in a group or undertaking	the leading comedian in a burlesque show
	the most important person in a group or undertaking