Lacking sound reasoning (9)
I believe the answer is:
illogical
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lacking sound reasoning</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 illogical that I've seen before include "Unreasonable" , "Lacking sound reasoning" , "not following" , "Irrational" , "Without reason" .)