arms vs armament

arms and armament both are nouns.

Word	Noun	Adjective	Verb	Adverb
arms	Yes	No	No	No
armament	Yes	No	No	No

As nouns, armament is a hyponym of arms; that is, armament is a word with a more specific, narrower meaning than arms:

arms (noun)	armament (noun)
weapons considered collectively	the act of equipping with weapons in preparation for war
the official symbols of a family, state, etc.	weaponry used by military or naval force