Not thin (3)
I believe the answer is:
fat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not thin</span>' is the definition.<br/ ><span class="explanation-format__explanation">('fat' is the opposite to 'thin')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for fat that I've seen before include "eg Lard" , "Obese, having spare tyre etc" , "and 24: Overpaid City type" , "Like 10 ac" , "Obese, overweight" .)