yam vs tuber

yam and tuber both are nouns.

Word	Noun	Adjective	Verb	Adverb
yam	Yes	No	No	No
tuber	Yes	No	No	No

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

yam: edible tuber of any of several yams
tuber: a fleshy underground stem or root serving for reproductive and food storage

yam (noun)	tuber (noun)
sweet potato with deep orange flesh that remains moist when baked	a fleshy underground stem or root serving for reproductive and food storage
edible tuberous root of various yam plants of the genus Dioscorea grown in the tropics world-wide for food
any of a number of tropical vines of the genus Dioscorea many having edible tuberous roots
edible tuber of any of several yams