heraldry vs arms

heraldry and arms both are nouns.

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

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

Other hyponyms of heraldry include armorial bearing, bearing, charge, heraldic bearing, blazon, blazonry, coat of arms.

heraldry (noun)	arms (noun)
emblem indicating the right of a person to bear arms	weapons considered collectively
the study and classification of armorial bearings and the tracing of genealogies	the official symbols of a family, state, etc.