shirtfront vs plastron

shirtfront and plastron both are nouns.

Word	Noun	Adjective	Verb	Adverb
shirtfront	Yes	No	No	No
plastron	Yes	No	No	No

As nouns, plastron is a hyponym of shirtfront; that is, plastron is a word with a more specific, narrower meaning than shirtfront:

shirtfront (noun)	plastron (noun)
a man's detachable insert (usually starched) to simulate the front of a shirt	(zoology) the part of a turtle's shell forming its underside
the front of a shirt (usually the part not covered by a jacket)	a large pad worn by a fencer to protect the chest
	a metal breastplate that was worn under a coat of mail
	the front of man's dress shirt
	the ornamental front of a woman's bodice or shirt