mashed potato vs white potato

mashed potato and white potato both are nouns.

Word	Noun	Adjective	Verb	Adverb
mashed potato	Yes	No	No	No
white potato	Yes	No	No	No

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

mashed potato: potato that has been peeled and boiled and then mashed
white potato: an edible tuber native to South America; a staple food of Ireland

Other hypernyms of mashed potato include Irish potato, murphy, potato, spud, tater.

mashed potato (noun)	white potato (noun)
potato that has been peeled and boiled and then mashed	an edible tuber native to South America; a staple food of Ireland
	annual native to South America having underground stolons bearing edible starchy tubers; widely cultivated as a garden vegetable; vines are poisonous