Weakened anew, perhaps, to a bad end (5)
I believe the answer is:
waned
'weakened' is the definition.
(I've seen this in another clue)
'anew perhaps to a bad end' is the wordplay.
'perhaps' indicates anagramming the letters.
'to' is a charade indicator (letters next to each other).
'end' indicates one should take the final letters.
The final letter of 'bad' is 'd'.
'anew' with letters rearranged gives 'wane'.
'wane'+'d'='WANED'
(Other definitions for waned that I've seen before include "(Of moon) grew smaller" , "Decreased in size" , "grew faint" , "Ebbed; declined" .)