Listen secretly (9)
I believe the answer is:
eavesdrop
'listen secretly' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eavesdrop that I've seen before include "Listen secretly to a private conversation" , "Listen secretly to others' conversations" , "Overhear" , "Listen at windows" , "Listen to others' conversation" .)