Failing, defect (5)
I believe the answer is:
fault
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">failing</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">defect</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for fault that I've seen before include "Geological strata dislocation" , "Censure" , "Flaw - defect" , "Defect or offence" , "Defect; culpability" .)