Opera villainess, often (4)
I believe the answer is:
alto
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">opera villainess often</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 alto that I've seen before include "Highest male voice: lowest female voice" , "Singing range" , "Lowest female singing voice" , "Singer's hidden inside chemical toilet" , "Key old > male who scores high" .)