gusset

noun

1. a small, triangular piece of material inserted into a shirt, shoe, etc., to improve the fit or for reinforcement.Compare godet(def 1), gore³(def 1).
2. Civil Engineering. a plate for uniting structural members at a joint, as in a steel frame or truss.
3. Armor.
   1. Also called voider.an area of mail backed with cloth, for defending the armpits or areas at joints.
   2. a small piece of plate armor at the armhole of a cuirass; pallet.

noun

1. an inset piece of material used esp to strengthen or enlarge a garment
2. a triangular metal plate for strengthening a corner joist between two structural members
3. a piece of mail fitted between armour plates or into the leather or cloth underclothes worn with armour, to give added protection

verb

4. (tr) to put a gusset in (a garment)