Curved part of the foot (4)
I believe the answer is:
arch
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">curved part of the foot</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 arch that I've seen before include "Structure with a keystone" , "Marble, for example" , "Chief: crafty" , "Curved span" , "Bridge span" .)