Origin of tuber? (4)
I believe the answer is:
root
I believe this is a double definition.
'origin' is the first definition.
(I know that origin can be written as root)
'tuber?' is the second definition.
(I've seen this in another clue)
'of' acts as a link.
(Other definitions for root that I've seen before include "could be square" , "Tuber" , "Origin - stem" , "support" , "grub" .)