root vegetable vs veg

root vegetable and veg both are nouns.

Word	Noun	Adjective	Verb	Adverb
root vegetable	Yes	No	No	No
veg	Yes	No	No	No

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

root vegetable: any of various fleshy edible underground roots or tubers
veg: edible seeds or roots or stems or leaves or bulbs or tubers or nonsweet fruits of any of numerous herbaceous plant

Other hypernyms of root vegetable include vegetable, veggie.

root vegetable (noun)	veg (noun)
any of various fleshy edible underground roots or tubers	edible seeds or roots or stems or leaves or bulbs or tubers or nonsweet fruits of any of numerous herbaceous plant