Pilotless plane (5)
I believe the answer is:
drone
'pilotless plane' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for drone that I've seen before include "Low hum; parasite" , "Bertie Wooster, say" , "Lounger" , "boring speaker" , "talk long and tediously" .)