By ear (5)
I believe the answer is:
aural
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">by ear</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 aural that I've seen before include "but not in the nose!" , "Received by the ears" , "of air" , "To do with an ear or hearing" , "Pertaining to the ear" .)