Knuckle under (7)
I believe the answer is:
succumb
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">knuckle under</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for succumb that I've seen before include "Fail to resist (temptation, perhaps)" , "Give in (to disease, etc)" , "Give in, yield" , "Surrender" , "Gives in under pressure, capitulates" .)