Completely preoccupy (6)
I believe the answer is:
obsess
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">completely preoccupy</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for obsess that I've seen before include "Prey on" , "Bosses (anag.)" , "Control" , "Be constantly talking about" , "brood" .)