First, second or reverse (4)
I believe the answer is:
gear
'first second or reverse' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gear that I've seen before include "Toothed wheel and youthful fashion" , "Clothing - tackle" , "Equipment - changed in the car?" , "Illicit drugs (slang) - kit" , "Cogwheel - equipment" .)