Keep hold of (6)
I believe the answer is:
retain
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">keep hold of</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 retain that I've seen before include "Keep; remember" , "Not relinquish" , "'Hold, keep back (6)'" , "Keep in place" , "Keep, hold on to something" .)