Unknown Soldier vs soldier

Unknown Soldier and soldier both are nouns.

Word	Noun	Adjective	Verb	Adverb
Unknown Soldier	Yes	No	No	No
soldier	Yes	No	Yes	No

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

Unknown Soldier: an unidentified soldier whose body is honored as a memorial
soldier: an enlisted man or woman who serves in an army

Unknown Soldier (noun)	soldier (noun)
an unidentified soldier whose body is honored as a memorial	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

Unknown Soldier (verb)	soldier (verb)
	serve as a soldier in the military