Possibly lose the blackthorn (4)
I believe the answer is:
sloe
'the blackthorn' is the definition.
(synonyms)
'possibly lose' is the wordplay.
'possibly' is an anagram indicator.
'lose' with letters rearranged gives 'SLOE'.
(Other definitions for sloe that I've seen before include "Sour blue-black fruit" , "Black fruit" , "Fruit often used for gin" , "Musical study" , "Thorny bush with plum-like fruit" .)