Achilles' weak spot (4)
I believe the answer is:
heel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">achilles' weak spot</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 heel that I've seen before include "despicable person" , "tip" , "Slang scoundrel or rear of foot" , "See 1 down" , "swine" .)