False, sham (6)
I believe the answer is:
pseudo
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">false</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">sham</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that sham can be written as pseudo)</span><br/ ><br/ ></span>
(Other definitions for pseudo that I've seen before include "Dose up (anag.); pretentious" , "Prefix for fake" , "Fake, pretentious" , "Not genuine" , "Counterfeit" .)