Walk with heavy steps
'walk with heavy steps' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for plod that I've seen before include "Tread wearily" , "Walk slowly and laboriously" , "Trudge - policeman" , "Shamus, say" , "Walk along heavily" .)
(Other definitions for trudge that I've seen before include "Plod wearily" , "Clump" , "tramp" , "Traipse" , "March joylessly" .)