Misty zone covered in grass (4)
I believe the answer is:
hazy
'misty' is the definition.
(I know that misty can be written as hazy)
'zone covered in grass' is the wordplay.
'zone' becomes 'z'.
'covered in' means one lot of letters goes inside another.
'grass' becomes 'hay' (hay is dried grass).
'z' inserted into 'hay' is 'HAZY'.
(Other definitions for hazy that I've seen before include "Nebulous" , "Slightly misty, vague" , "Affected by mist - indistinct" , "Blurred" , "Vague, ill-defined" .)