Lowest high tide (4)
I believe the answer is:
neap
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lowest high tide</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 neap that I've seen before include "The middle-sized tide" , "Least in difference between high and low tides" , "Of smallest tidal range" , "Small tide" , "It's between spring and ebb" .)