Sucking up (9)
I believe the answer is:
absorbing
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sucking up</span>' is the definition.<br/ ><span class="explanation-format__explanation">('absorb' can be a synonym of 'suck up')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for absorbing that I've seen before include "Eating in" , "most entertaining" , "Engrossing" .)