Evacuated station with long grass (6)
I believe the answer is:
snitch
'grass' is the definition.
(both mean to inform on or betray)
'evacuated station with long' is the wordplay.
'evacuated' says to hollow out the word (remove centre letters).
'with' means one lot of letters go next to another.
'long' becomes 'itch' (I've seen this before).
'station' with its middle removed is 'sn'.
'sn'+'itch'='SNITCH'
(Other definitions for snitch that I've seen before include "Police informer" , "Inform on, tell tales" , "I'm telling!" , "Steal; inform (on someone)" , "Inform on someone in slangy way" .)