mashed potato vs Irish potato

mashed potato and Irish potato both are nouns.

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

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

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

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

mashed potato (noun)	Irish potato (noun)
potato that has been peeled and boiled and then mashed	an edible tuber native to South America; a staple food of Ireland