bowling pin vs kingpin

bowling pin and kingpin both are nouns.

Word	Noun	Adjective	Verb	Adverb
bowling pin	Yes	No	No	No
kingpin	Yes	No	No	No

As nouns, kingpin is a hyponym of bowling pin; that is, kingpin is a word with a more specific, narrower meaning than bowling pin:

bowling pin: a club-shaped wooden object used in bowling; set up in triangular groups of ten as the target
kingpin: the front bowling pin in the triangular arrangement of ten pins

Other hyponyms of bowling pin include candlepin, duckpin, headpin, ninepin, skittle, skittle pin, tenpin.

bowling pin (noun)	kingpin (noun)
a club-shaped wooden object used in bowling; set up in triangular groups of ten as the target	bolt that provides a steering joint in a motor vehicle
	the front bowling pin in the triangular arrangement of ten pins
	the most important person in a group or undertaking