Hard edible seed (3)
I believe the answer is:
nut
'hard edible seed' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for nut that I've seen before include "eg Hazel" , "Large, hard-shelled seed" , "Bonce" , "Lover < or partner to bolt f" , "Somebody obsessed" .)