Err, fail (2,5)
I believe the answer is:
go wrong
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">err</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(going wrong is a kind of erring)</span><br/ ><br/ >'<span class="explanation-format__original">fail</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for go wrong that I've seen before include "Misfunction" , "Make a mistake" .)