kingpin vs top banana

kingpin and top banana both are nouns.

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

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

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

Other synonyms of kingpin include bigwig.

kingpin (noun)	top banana (noun)
bolt that provides a steering joint in a motor vehicle	the leading comedian in a burlesque show
the front bowling pin in the triangular arrangement of ten pins	the most important person in a group or undertaking
the most important person in a group or undertaking