Brief swim (3)
I believe the answer is:
dip
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">brief swim</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 dip that I've seen before include "An informal swim or a downward slope" , "Plunge briefly in liquid" , "Duck" , "Sink; thick sauce" , "Sink; immerse" .)