Nautical hail (4)
I believe the answer is:
ahoy
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nautical hail</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ahoy that I've seen before include "Seafarer's call" , "Mariner's challenge" , "Call for ship's attention" , "Nautical shout" , "Hullo, sailor!" .)