Sail a zigzag course (4)
I believe the answer is:
tack
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sail a zigzag course</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 tack that I've seen before include "policy" , "Type of nail" , "Ship's course; horse's harness" , "Drawing-pin" , "Turn and sail into the wind" .)