gusset
n.
5ME guschet < OFr gousset6
1 a piece of chain mail or a metal plate protecting the opening of a joint in a suit of armor
2 a triangular or diamond-shaped piece inserted in a garment, glove, etc. to make it stronger or roomier
3 a brace, usually triangular, for reinforcing a corner or angle in the framework of a structure
vt.
to furnish with a gusset