sun vs sunburst

sun and sunburst both are nouns.

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

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

sun (noun)	sunburst (noun)
any star around which a planetary system revolves	a jeweled brooch with a pattern resembling the sun
the star that is the source of light and heat for the planets in the solar system	a design consisting of a central disk resembling the sun and rays emanating from it
a person considered as a source of warmth or energy or glory etc	a sudden emergence of the sun from behind clouds
the rays of the sun

sun (verb)	sunburst (verb)
expose one's body to the sun
expose to the rays of the sun or affect by exposure to the sun