Prefix for "pilot" (4)
I believe the answer is:
auto
'prefix for pilot' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for auto that I've seen before include "Prefix meaning self or same" , "Prefix denoting by or of the same person or thing" , "Motor car (mainly US)" , "Car (mostly US)" , "Prefix to denote self or same" .)