Being untruthful (5)
I believe the answer is:
lying
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">being untruthful</span>' is the definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lying that I've seen before include "Deviating from truth" , "Flat" , "Extending" , "Deceitful" , "Deceit" .)