Mountain air? (5)
I believe the answer is:
yodel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mountain air?</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 yodel that I've seen before include "make an off-peak call" , "Sing (in the Alps)" , "Sing like the Lonely Goatherd?" , "Sing in Tyrolean fashion" , "Sing (Swiss style)" .)