Imaginary, illusory (6)
I believe the answer is:
unreal
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">imaginary</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">illusory</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ ></span>
(Other definitions for unreal that I've seen before include "Not actual or credible" , "Not genuine" , "fake" , "Dreamlike" , "Not actually existing" .)