chain armour vs chain mail

chain armour and chain mail both are nouns.

Word	Noun	Adjective	Verb	Adverb
chain armour	Yes	No	No	No
chain mail	Yes	No	No	No

As nouns, chain armour and chain mail are synonyms defined as:

chain armour and chain mail: (Middle Ages) flexible armor made of interlinked metal rings

Other synonyms of chain armour include chain armor, mail, ring armor, ring armour, ring mail.

chain armour (noun)	chain mail (noun)
(Middle Ages) flexible armor made of interlinked metal rings	(Middle Ages) flexible armor made of interlinked metal rings