Thanksgiving tuber (3)
I believe the answer is:
yam
'thanksgiving tuber' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for yam that I've seen before include "May be a sweet potato" , "vegetable plant" , "Potato-like vegetable" , "A starchy tuber" , "May be a sweet spud" .)