sunbonnet vs sun hat

sunbonnet and sun hat both are nouns.

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

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

sunbonnet: a large bonnet that shades the face; worn by girls and women
sun hat: a hat with a broad brim that protects the face from direct exposure to the sun

Other hypernyms of sunbonnet include bonnet, poke bonnet, sunhat.

sunbonnet (noun)	sun hat (noun)
a large bonnet that shades the face; worn by girls and women	a hat with a broad brim that protects the face from direct exposure to the sun