Remain silent (4,3)
I believe the answer is:
keep mum
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">remain silent</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for keep mum that I've seen before include "Don't tell a soul" , "Remain silent" , "(don't mention it)" , "Stay silent" .)