Gusset \Gus"set\, n. [F. gousset armpit, fob, gusset, dim. of gousse pod, husk; cf. It. guscio shell, or W. cwysed gore, gusset.]

1. A small piece of cloth inserted in a garment, for the purpose of strengthening some part or giving it a tapering enlargement.

Seam and gusset and band. --Hood.

2. Anything resembling a gusset in a garment; as:
   (a) (Armor) A small piece of chain mail at the openings of the joints beneath the arms.
   (b) (Mach.) A kind of bracket, or angular piece of iron, fastened in the angles of a structure to give strength or stiffness; esp., the part joining the barrel and the fire box of a locomotive boiler.

3. (Her.) An abatement or mark of dishonor in a coat of arms, resembling a gusset.

Source: Webster's Revised Unabridged Dictionary (1913)