Grumbler (6)
'grumbler' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sourpuss that I've seen before include "Miserable so-and-so" , "Habitually sullen person" , "crab" , "Habitually gloomy person" , "One has a habitually sullen expression" .)
'grumbler' is the definition.
(I know that grumbler can be written as moaner)
This is the entire clue.
(Other definitions for moaner that I've seen before include "Grouch" , "Complainer" , "Grumbler" , "One who complains" .)