Informant on the lawn (5)
I believe the answer is:
grass
I believe this clue is a double definition.
'informant' is the first definition.
(term for an informant or traitor)
'the lawn' is the second definition.
(I've seen this before)
'on' acts as a link.
(Other definitions for grass that I've seen before include "Turf" , "often walked over in court" , "Shopper" , "blades" , "Soporific" .)