Reinforced Piece of Fabric Especially in Underwear
Puzzle 19 of Good luck Easy Pack
Question is: Reinforced Piece of Fabric Especially in Underwear
and the answer is: GUSSET
Word Meaning:
GUSSET — A small piece of cloth inserted in a garment, for the purpose of strengthening some part or giving it a tapering enlargement cf. godet.
Definitions from Wiktionary.