Not sensible (11)
I believe the answer is:
impractical
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not sensible</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 impractical that I've seen before include "Unworkable" , "Not sensible" , "That's not much use" , "Unrealistic" .)