infantryman vs foot soldier

infantryman and foot soldier both are nouns.

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

As nouns, infantryman and foot soldier are synonyms defined as:

Other synonyms of infantryman include footslogger, marcher.

infantryman (noun)	foot soldier (noun)
fights on foot with small arms	fights on foot with small arms
	an assistant subject to the authority or control of another