gusset vs chain mail

gusset and chain mail both are nouns.

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

As nouns, chain mail is a hypernym of gusset; that is, chain mail is a word with a broader meaning than gusset:

Other hypernyms of gusset include chain armor, chain armour, mail, ring armor, ring armour, ring mail.

gusset (noun)	chain mail (noun)
a piece of material used to strengthen or enlarge a garment	(Middle Ages) flexible armor made of interlinked metal rings
a metal plate used to strengthen a joist
a piece of chain mail covering a place unprotected by armor plate