Potato or yam (5)
I believe the answer is:
tuber
'potato or yam' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tuber that I've seen before include "A brute of a spud" , "Fleshy underground root" , "Thickened underground stem" , "Brute (anag)" , "Potato, for example" .)