Opera singers (6)
I believe the answer is:
tenors
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">opera singers</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 tenors that I've seen before include "Male singers with high register" , "Opera singers" , "Male singing voices" , "Male singers from Reston" .)