Number of Muses (4)
I believe the answer is:
nine
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">number of muses</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 nine that I've seen before include "Days Lady Jane 5 ac reigned" , "One's married partner" , "One over the eight" , "SECOND PART OF 14" , "One more than fourteen across" .)