army vs armed service

army and armed service both are nouns.

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

As nouns, armed service is a hypernym of army; that is, armed service is a word with a broader meaning than army:

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

Other hypernyms of army include military service, service.

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