Perceptive eavesdropping is futile (2-3)
I believe the answer is:
no-win
'futile' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for no-win that I've seen before include "Denoting situation in which success is impossible" , "Certain to end in failure" .)