white potato vs root vegetable

white potato and root vegetable both are nouns.

Word	Noun	Adjective	Verb	Adverb
white potato	Yes	No	No	No
root vegetable	Yes	No	No	No

As nouns, root vegetable is a hypernym of white potato; that is, root vegetable is a word with a broader meaning than white potato:

white potato: an edible tuber native to South America; a staple food of Ireland
root vegetable: any of various fleshy edible underground roots or tubers

Other hypernyms of white potato include starches, solanaceous vegetable.

white potato (noun)	root vegetable (noun)
an edible tuber native to South America; a staple food of Ireland	any of various fleshy edible underground roots or tubers
annual native to South America having underground stolons bearing edible starchy tubers; widely cultivated as a garden vegetable; vines are poisonous