armor vs coat of mail

armor and coat of mail both are nouns.

Word	Noun	Adjective	Verb	Adverb
armor	Yes	No	Yes	No
coat of mail	Yes	No	No	No

As nouns, coat of mail is a hyponym of armor; that is, coat of mail is a word with a more specific, narrower meaning than armor:

Other hyponyms of armor include body armor, body armour, cataphract, suit of armor, suit of armour, buckler, shield.

armor (noun)	coat of mail (noun)
tough more-or-less rigid protective covering of an animal or plant	armor that protects the wearer's whole body
protective covering made of metal and used in combat
a military unit consisting of armored fighting vehicles

armor (verb)	coat of mail (verb)
equip with armor