Half of evergreen bark (4)
I believe the answer is:
rind
'bark' is the definition.
(I've seen this in another clue)
'half of evergreen' is the wordplay.
'half of' means to take half the letters.
'evergreen' becomes 'tamarind' (I've seen this before).
'tamarind' cut in half is 'RIND'.
(Other definitions for rind that I've seen before include "Skin of bacon" , "The peel of a fruit" , "outside" , "'Peel, bark (4)'" , "Cheese or fruit skin" .)