Lion's hair
I believe the answer is:
mane
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lion's hair</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 mane that I've seen before include "Lion or horse's 10 Across" , "Name for hair on horse's neck" , "Animal neck-hair" , "Animal's neck hair" , "Neck hair of an animal" .)