Puzzle, riddle (6)
I believe the answer is:
enigma
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">puzzle</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">riddle</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that riddle can be written as enigma)</span><br/ ><br/ ></span>
(Other definitions for enigma that I've seen before include "Solution to mystery" , "Mystery U puzzle" , "Mysterious puzzle" , "Gamine being a bit of a puzzle" , "WW2 code" .)