Slog, hike (4)
I believe the answer is:
trek
I believe this is a double definition.
'slog' is the first definition.
(I've seen this before)
'hike' is the second definition.
(trekking is a kind of hiking)
(Other definitions for trek that I've seen before include "Long difficult walk" , "Difficult journey on foot" , "Tramp" , "Extended journey" , "A long arduous walk" .)