Large inlet (4)
I believe the answer is:
gulf
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">large inlet</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for gulf that I've seen before include "Rift" , "Large deep bay" , "Wide difference of opinion" , "Deep sea inlet, as between Iran and Saudi Arabia" , "Wide gap; arm of sea" .)