foot soldier vs underling

foot soldier and underling both are nouns.

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

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

foot soldier and underling: an assistant subject to the authority or control of another

Other synonyms of foot soldier include subordinate, subsidiary.

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