infantryman vs soldier

infantryman and soldier both are nouns.

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

As nouns, soldier is a hypernym of infantryman; that is, soldier is a word with a broader meaning than infantryman:

infantryman (noun)	soldier (noun)
fights on foot with small arms	a wingless sterile ant or termite having a large head and powerful jaws adapted for defending the colony
	an enlisted man or woman who serves in an army

infantryman (verb)	soldier (verb)
	serve as a soldier in the military