Informant to come down to pasture (9)
I believe the answer is:
grassland
'pasture' is the definition.
(I've seen this before)
'informant to come' is the wordplay.
'informant' becomes 'grass' (term for an informant or traitor).
'to' says to put letters next to each other.
'come' becomes 'land' (landing is a kind of coming).
'grass'+'land'='GRASSLAND'
'down to' is the link.
(Other definitions for grassland that I've seen before include "Meadow or prairie" , "pasture" , "(growth area)" , "Plain" , "green countryside" .)