Circumference, waistline (5)
I believe the answer is:
girth
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">circumference</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that girth is a type of circumference)</span><br/ ><br/ >'<span class="explanation-format__original">waistline</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for girth that I've seen before include "Measure all round" , "Distance round the middle" , "Personal circumference" , "Distance around, often of the tummy" , "Perimeter" .)