headpin vs kingpin

headpin and kingpin both are nouns.

Word	Noun	Adjective	Verb	Adverb
headpin	Yes	No	No	No
kingpin	Yes	No	No	No

As nouns, headpin and kingpin are synonyms defined as:

headpin and kingpin: the front bowling pin in the triangular arrangement of ten pins

headpin (noun)	kingpin (noun)
the front bowling pin in the triangular arrangement of ten pins	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