hat vs high hat

hat and high hat both are nouns.

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

As nouns, high hat is a hyponym of hat; that is, high 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
high hat: a man's hat with a tall crown; usually covered with silk or with beaver fur

hat (noun)	high hat (noun)
an informal term for a person's role	cymbals that are operated by a foot pedal
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

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