straw hat vs chapeau

straw hat and chapeau both are nouns.

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

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

straw hat: a stiff hat made of straw with a flat crown
chapeau: headdress that protects the head from bad weather; has shaped crown and usually a brim

Other hypernyms of straw hat include hat, lid.

straw hat (noun)	chapeau (noun)
a stiff hat made of straw with a flat crown	headdress that protects the head from bad weather; has shaped crown and usually a brim