hat vs silk hat

hat and silk hat both are nouns.

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

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

hat: 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

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

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