top banana vs kingpin

top banana and kingpin both are nouns.

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

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

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

Other synonyms of top banana include bigwig.

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