sun hat vs pith hat

sun hat and pith hat both are nouns.

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

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

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

Other hyponyms of sun hat include pith helmet, sun helmet, topee, topi, sunbonnet.

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