"That's odd" (5)
I believe the answer is:
weird
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">that's odd</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 weird that I've seen before include "Strange, peculiar" , "behaving erratically?" , "Rum" , "Quirky" , "Creepy" .)