Outdoor swimming pool (4)
I believe the answer is:
lido
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">outdoor swimming pool</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for lido that I've seen before include "Public open swimming pool" , "Outdoor swimming pool" , "Venetian resort" , "Idol (anag.)" , "bathing-beach" .)