Mountain lake (4)

I believe the answer is:
tarn
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mountain lake</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 tarn that I've seen before include "High water" , "Small mountain lake" , "Mountain pool: French department" , "Scottish mountain lake" .)