Informer with boy going round north prairie (9)
I believe the answer is:
grassland
'prairie' is the definition.
(thesaurus)
'informer with boy going round north' is the wordplay.
'informer' becomes 'grass' (grass can mean an informant).
'with' is a charade indicator (letters next to each other).
'boy' becomes 'lad' (informal term for boy).
'going round' is an insertion indicator (some letters go around others).
'north' becomes 'N' (abbreviation).
'lad' going around 'n' is 'land'.
'grass'+'land'='GRASSLAND'
(Other definitions for grassland that I've seen before include "Plain" , "Meadow or prairie" , "Large area suitable for grazing" , "pasture" , "green countryside" .)