Moan, grumble (6)
I believe the answer is:
whinge
I believe this clue is a double definition.
'moan' is the first definition.
(I've seen this before)
'grumble' is the second definition.
(I've seen this before)
(Other definitions for whinge that I've seen before include "Whine and grumble persistently" , "Hewing (anag.)" , "Complain, whine" , "Grumble or complain persistently" , "Complain peevishly" .)