Underside of the foot (4)
I believe the answer is:
sole
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">underside of the foot</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sole that I've seen before include "Lone; part of foot" , "fish > that's never less than foot in length" , "Kind of fish - lose it" , "Fish; part of foot" , "piece of leather" .)