Acorn or cashew (3)
I believe the answer is:
nut
I believe this is a double definition.
'acorn' is the first definition.
(I've seen this in another clue)
'cashew' is the second definition.
(I've seen this in another clue)
(Other definitions for nut that I've seen before include "Headcase" , "Enthusiast (slang)" , "Large, hard-shelled seed" , "Screwball" , "Lover < or partner to bolt f" .)