"Hello, sailor!" (4)
I believe the answer is:
ahoy
'hello sailor' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ahoy that I've seen before include "Cry at sea" , "Call for ship's attention" , "Nautical shout" , "Nautical call for attention" , "Hail at sea" .)