pith hat vs sun hat

pith hat and sun hat both are nouns.

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

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

pith hat: a lightweight hat worn in tropical countries for protection from the sun
sun hat: a hat with a broad brim that protects the face from direct exposure to the sun

Other hypernyms of pith hat include sunhat.

pith hat (noun)	sun hat (noun)
a lightweight hat worn in tropical countries for protection from the sun	a hat with a broad brim that protects the face from direct exposure to the sun