Yams and potatoes (6)
I believe the answer is:
tubers
'yams and potatoes' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tubers that I've seen before include "Oddly rebuts the potatoes and dahlias" , "Potatoes and dahlias, say" , "Kind of potatoes - real brutes (6)" , "Wrongly rebuts the potatoes, say" , "spuds etc" .)