A street breaking into unspoilt farmland (7)
I believe the answer is:
pasture
'farmland' is the definition.
(thesaurus)
'a street breaking into unspoilt' is the wordplay.
'street' becomes 'st' (abbreviation).
'breaking into' is an insertion indicator.
'unspoilt' becomes 'pure'.
'a'+'st'='ast'
'ast' placed inside 'pure' is 'PASTURE'.
(Other definitions for pasture that I've seen before include "Meadow" , "Land for grazing cattle" , "Grass for grazing" , "Field suitable for grazing" , "Meadowland" .)