Tuber, in spring time, coming from the east (3)
I believe the answer is:
yam
'tuber' is the definition.
(yam is a kind of tuber)
'spring time coming from the east' is the wordplay.
'spring time' becomes 'may' (I've seen this in another clue).
'coming from the east' shows that the letters should be reversed in order (letters written from right to left or east to west).
'may' backwards is 'YAM'.
'in' acts as a link.
(Other definitions for yam that I've seen before include "Tropical climber" , "Edible tuber" , "vegetable plant" , "US sweet-potato" , "Potato-like vegetable" .)