casquet vs casque

casquet and casque both are nouns.

Word	Noun	Adjective	Verb	Adverb
casquet	Yes	No	No	No
casque	Yes	No	No	No

As nouns, casque is a hypernym of casquet; that is, casque is a word with a broader meaning than casquet:

casquet: a light open casque without a visor or beaver
casque: (15-16th century) any armor for the head; usually ornate without a visor

casquet (noun)	casque (noun)
a light open casque without a visor or beaver	(15-16th century) any armor for the head; usually ornate without a visor