cowboy hat vs chapeau

cowboy hat and chapeau both are nouns.

Word	Noun	Adjective	Verb	Adverb
cowboy hat	Yes	No	No	No
chapeau	Yes	No	No	No

As nouns, chapeau is a hypernym of cowboy hat; that is, chapeau is a word with a broader meaning than cowboy hat:

cowboy hat: a hat with a wide brim and a soft crown; worn by American ranch hands
chapeau: headdress that protects the head from bad weather; has shaped crown and usually a brim

Other hypernyms of cowboy hat include hat, lid.

cowboy hat (noun)	chapeau (noun)
a hat with a wide brim and a soft crown; worn by American ranch hands	headdress that protects the head from bad weather; has shaped crown and usually a brim