foot soldier vs soldier

foot soldier and soldier both are nouns.

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

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

foot soldier (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 assistant subject to the authority or control of another	an enlisted man or woman who serves in an army

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