Golfer's alert (4)
I believe the answer is:
fore
'golfer's alert' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fore that I've seen before include "Warning cry on a golf course" , "The front part of a ship" , "Golfer's warning shout" , "Towards the front of a ship" , "Fairway warning" .)