Was first in double-dealing (3)
I believe the answer is:
led
'was first' is the definition.
(to lead is to go first)
'in double-dealing' is the wordplay.
'in' indicates a hidden word.
'LED' can be found hidden inside 'double dealing'.
(Other definitions for led that I've seen before include "showed the way ahead" , "Came first" , "Light-emitting diode (abbr.)" , "was in the van" , "Shown the way" .)