Piece of material used to enlarge a garment (6)
I believe the answer is:
gusset
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">piece of material used to enlarge a garment</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for gusset that I've seen before include "Guests (anag.)" , "Piece of material set into a dress" , "Piece of inserted material" , "Gets us (anag.)" , "Garment enlarger" .)