armed service vs army

armed service and army both are nouns.

Word	Noun	Adjective	Verb	Adverb
armed service	Yes	No	No	No
army	Yes	No	No	No

As nouns, army is a hyponym of armed service; that is, army is a word with a more specific, narrower meaning than armed service:

armed service: a force that is a branch of the armed forces
army: a permanent organization of the military land forces of a nation or state

Other hyponyms of armed service include ground forces, regular army, naval forces, navy, coastguard, Marines, air force, airforce.

armed service (noun)	army (noun)
a force that is a branch of the armed forces	a permanent organization of the military land forces of a nation or state
	a large number of people united for some specific purpose