Song thrush (5)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">song thrush</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mavis that I've seen before include "Fem. name, song thrush" , "Girl" , "bird" , "Girl's name - song thrush" .)