Achilles' weak point (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">achilles' weak point</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for heel that I've seen before include "Achilles's weak spot" , "See 21" , "bank" , "Slang scoundrel or rear of foot" , "Crusty end of a loaf" .)