Very much dead under the earth (3)
I believe the answer is:
sod
'the earth' is the definition.
(I've seen this before)
'very much dead under' is the wordplay.
'very much' becomes 'so'.
'dead' becomes 'd'.
'under' is a charade indicator (letters next to each other).
'so'+'d'='SOD'
(Other definitions for sod that I've seen before include "A lump of turf (3)" , "Surface layer of ground with grass roots" , "A lulmp of turf" , "Piece of peat or grass" , "Lump of earth" .)