Half sodden turf (3)
I believe the answer is:
sod
'turf' is the definition.
('sod' can be a synonym of 'turf')
'half sodden' is the wordplay.
'half' suggests halving the letters.
'sodden' cut in half is 'SOD'.
(Other definitions for sod that I've seen before include "A lulmp of turf" , "Piece of ground with a mat of grass" , "Piece of grassy soil" , "A lump of turf (3)" , "Lump of earth" .)