Backless slipper (4)
I believe the answer is:
mule
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">backless slipper</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 mule that I've seen before include "Equine hybrid" , "Offspring of a donkey and a mare" , "on foot?" , "Obstinate person?" , "Obstinate quadruped" .)