Curious thing (6)
I believe the answer is:
oddity
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">curious thing</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 oddity that I've seen before include "Something strange or peculiar" , "Family relative" , "rare thing" , "Something unusual or curious" , "Something strange or unusual" .)