Might return yam (3)
I believe the answer is:
may
'might' is the definition.
(I've seen this in another clue)
'return yam' is the wordplay.
'return' says the letters should be written in reverse.
'yam' back-to-front is 'MAY'.
(Other definitions for may that I've seen before include "Girl's name; 10 ac (anag.)" , "Month - tree" , "plant that's tropical making comeback" , "UK PM" , "Might" .)