hat vs sun hat

hat and sun hat both are nouns.

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

As nouns, sun hat is a hyponym of hat; that is, sun 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
sun hat: a hat with a broad brim that protects the face from direct exposure to the sun

hat (noun)	sun hat (noun)
an informal term for a person's role	a hat with a broad brim that protects the face from direct exposure to the sun
headdress that protects the head from bad weather; has shaped crown and usually a brim

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