rock sugar vs refined sugar

rock sugar and refined sugar both are nouns.

Word	Noun	Adjective	Verb	Adverb
rock sugar	Yes	No	No	No
refined sugar	Yes	No	No	No

As nouns, refined sugar is a hypernym of rock sugar; that is, refined sugar is a word with a broader meaning than rock sugar:

rock sugar: sugar in the form of large crystals, often used for decoration.
refined sugar: a white crystalline carbohydrate used as a sweetener and preservative

Other hypernyms of rock sugar include sugar.

rock sugar (noun)	refined sugar (noun)
sugar in the form of large crystals, often used for decoration.	a white crystalline carbohydrate used as a sweetener and preservative