Drudge or trudge (4)
I believe the answer is:
plod
This clue is a double definition.
'drudge' is the first definition.
(I've seen this in another clue)
'trudge' is the second definition.
(I know that trudge can be written as plod)
(Other definitions for plod that I've seen before include "Heavy walk; PC (slang)" , "Shamus, say" , "Work (or walk) laboriously" , "Walk with heavy steps" , "Stomp" .)