Monster managed to share complaint (13)
I believe the answer is:
remonstration
'complaint' is the definition.
(thesaurus)
'monster managed to share' is the wordplay.
'managed' indicates anagramming the letters.
'to share' becomes 'ration' (a ration is a share of a limited resource).
'monster' is an anagram of 'remonst'.
'remonst'+'ration'='REMONSTRATION'
(Other definitions for remonstration that I've seen before include "Disapproval" , "protest" .)