Possibly beat a retreat (5)
I believe the answer is:
abate
'retreat' is the definition.
(I've seen this before)
'possibly beat a' is the wordplay.
'possibly' indicates anagramming the letters.
'beat'+'a'='beata'
'beata' with letters rearranged gives 'ABATE'.
(Other definitions for abate that I've seen before include "Subside, grow less" , "retreat" , "Ease off" , "Subside like storm" , "Become less intense" .)