Extremely fat (5)
I believe the answer is:
obese
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">extremely fat</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for obese that I've seen before include "Very substantial" , "Morbidly overweight" , "Falstaffian" , "Clinically overweight" , "Stout" .)