All-consuming idea (9)
I believe the answer is:
obsession
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">all-consuming idea</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 obsession that I've seen before include "Fixed idea" , "Phobia" , "Compulsion, fixation" , "Extreme interest" , "Continual preoccupation" .)