casque vs casquetel

casque and casquetel both are nouns.

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

As nouns, casquetel is a hyponym of casque; that is, casquetel 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
casquetel: a light open casque without a visor or beaver

Other hyponyms of casque include casquet.

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