Greenish nut (9)
I believe the answer is:
pistachio
'greenish nut' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pistachio that I've seen before include "Type of nut" , "Edible nut" , "Small sweet-tasting nut" , "nut-bearing tree" , "Yellowish-green" .)