chapeau vs silk hat

chapeau and silk hat both are nouns.

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

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

chapeau: headdress that protects the head from bad weather; has shaped crown and usually a brim
silk hat: a man's hat with a tall crown; usually covered with silk or with beaver fur

chapeau (noun)	silk hat (noun)
headdress that protects the head from bad weather; has shaped crown and usually a brim	a man's hat with a tall crown; usually covered with silk or with beaver fur