Passing fancy (4)
I believe the answer is:
whim
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">passing fancy</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 whim that I've seen before include "Fancy, notion" , "Impulse or caprice" , "Sudden odd desire" , "Sudden or capricious idea" , "Caprice, sudden fancy" .)