infantryman vs doughboy

infantryman and doughboy both are nouns.

Word	Noun	Adjective	Verb	Adverb
infantryman	Yes	No	No	No
doughboy	Yes	No	No	No

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

Other hyponyms of infantryman include fusilier, grenade thrower, grenadier, musketeer.

infantryman (noun)	doughboy (noun)
fights on foot with small arms	a rounded lump of dough that is deep-fried and served as hot bread
	an American infantryman in World War I