casque vs casquet

casque and casquet both are nouns.

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

As nouns, casquet is a hyponym of casque; that is, casquet is a word with a more specific, narrower meaning than casque:

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

Other hyponyms of casque include casquetel.

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