headdress vs hat

headdress and hat both are nouns.

Word	Noun	Adjective	Verb	Adverb
headdress	Yes	No	No	No
hat	Yes	No	Yes	No

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

headdress: clothing for the head
hat: headdress that protects the head from bad weather; has shaped crown and usually a brim

headdress (noun)	hat (noun)
clothing for the head	an informal term for a person's role
	headdress that protects the head from bad weather; has shaped crown and usually a brim

headdress (verb)	hat (verb)
	put on or wear a hat
	furnish with a hat