topping vs frosting

topping and frosting both are nouns.

Word	Noun	Adjective	Verb	Adverb
topping	Yes	Yes	No	No
frosting	Yes	No	No	No

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

Other hyponyms of topping include ice, icing, glaze, meringue, whipped cream, streusel.

topping (noun)	frosting (noun)
a flavorful addition on top of a dish	a flavored sugar topping used to coat and decorate cakes

topping (adjective)	frosting (adjective)
excellent; best possible