Unnatural, artificial (6)
I believe the answer is:
forced
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">unnatural</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">artificial</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for forced that I've seen before include "Compelled, made to obey" , "Compelled or strained" , "Compelled or obliged" , "Compelled, made to do something" , "Not natural" .)