Fallacious, illogical (7)
I believe the answer is:
unsound
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">fallacious</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">illogical</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for unsound that I've seen before include "Damaged" , "Unreliable; not healthy" , "silence?" , "Ill-founded" , "Unfit or unreliable" .)