Turf very damp at first (3)
I believe the answer is:
sod
'turf' is the definition.
(both can mean a piece of grass)
'very damp at first' is the wordplay.
'very' becomes 'so' (both can mean 'extremely').
'at first' suggests taking the first letters.
The initial letter of 'damp' is 'd'.
'so'+'d'='SOD'
(Other definitions for sod that I've seen before include "A lulmp of turf" , "Lump of earth" , "Lump of turf or unpleasant person" , "Piece of peat or grass" , "A piece of sward." .)