Narrow inlet (3)
I believe the answer is:
ria
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">narrow inlet</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ria that I've seen before include "Irish academy for sciences and humanities, in short" , "Long narrow inlet" , "inlet between hills" , "Drowned river valley now an inlet of the sea" , "Coastal inlet" .)