potato bean vs tuber

potato bean and tuber both are nouns.

Word	Noun	Adjective	Verb	Adverb
potato bean	Yes	No	No	No
tuber	Yes	No	No	No

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

potato bean: nutlike tuber; important food of Native Americans
tuber: a fleshy underground stem or root serving for reproductive and food storage

potato bean (noun)	tuber (noun)
nutlike tuber; important food of Native Americans	a fleshy underground stem or root serving for reproductive and food storage
a North American vine with fragrant blossoms and edible tubers; important food crop of Native Americans
twining plant of Amazon basin having large edible roots