Refuse, refute (4)
I believe the answer is:
deny
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">refuse</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that deny is a kind of keep back)</span><br/ ><br/ >'<span class="explanation-format__original">refute</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for deny that I've seen before include "Claim to be untrue" , "Disown" , "Refuse to acknowledge" , "Refuse access to" , "Refute, contradict" .)