chain armour vs chain armor

chain armour and chain armor both are nouns.

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

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

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

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

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