Retain possession of (4)
I believe the answer is:
keep
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">retain possession 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 keep that I've seen before include "Retain; strong tower" , "Remain" , "strong position" , "Central tower of castle" , "run" .)