Hog's grunt (4)
I believe the answer is:
mine
'hog's grunt' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mine that I've seen before include "Bomb - colliery" , "Excavate for minerals" , "Explosive device concealed in ground" , "Source of wealth" , "Excavation in the earth for digging coal etc" .)