Pasture with fine mature greenery (7)
I believe the answer is:
leafage
'greenery' is the definition.
(I've seen this before)
'pasture with fine mature' is the wordplay.
'pasture' becomes 'lea' (synonyms).
'with' says to put letters next to each other.
'fine' becomes 'f' (abbreviation).
'mature' becomes 'age' (synonyms).
'lea'+'f'+'age'='LEAFAGE'
(Other definitions for leafage that I've seen before include "marijuana, possibly" , "Gala fee (anag)" , "Green growth" , "Foliage" , "Greenery" .)