Retarded (8)
I believe the answer is:
backward
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">retarded</span>' is the definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for backward that I've seen before include "Diffident, making poor progress" , "Shy, bashful" , "Retiring" , "Direction to the rear" , "Bashful - in reverse" .)