armour vs coat of mail

armour and coat of mail both are nouns.

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

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

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

armour (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

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