Secretly remove radar that's directly above (4)
I believe the answer is:
over
'directly above' is the definition.
(I've seen this before)
'secretly remove radar that's' is the wordplay.
'secretly' says the answer is hidden in the clue.
'OVER' can be found hidden inside 'remove radar that'.
(Other definitions for over that I've seen before include "Period of play" , "Accomplished" , "Round of six bowls in cricket - then it's finished" , "See 12" , "Six balls, as a unit" .)