Mariner's cry (4)
I believe the answer is:
ahoy
'mariner's cry' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ahoy that I've seen before include "Temporarily blind" , "Sailor's call for attention" , "Cry at sea" , "A sailor's call to a ship" , "Naval call for attention" .)