Obsessive interest (8)
I believe the answer is:
fixation
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">obsessive interest</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 fixation that I've seen before include "Obsessive interest" , "Unhealthy preoccupation" , "Obsession" , "thing" .)