Nickname for Billie Holiday (4,3)
I believe the answer is:
lady day
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nickname for billie holiday</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lady day that I've seen before include "March twenty-fifth" , "March twenty five" , "Nickname of Billy Holiday" , "festival" , "25 March" .)