gusset

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A triangular insert, as in the seam of a garment, for added strength or expansion.
2. n. A triangular metal bracket used to strengthen a joist.
3. n. A piece of mail or plate armor protecting the joints in a suit of armor.

Century Dictionary and Cyclopedia

1. n. A triangular plate or piece of cloth inserted or attached, to protect, strengthen, or fill out some part of a thing; a gore. specifically — The triangular space left at each joint of the body between two adjacent pieces of plate-armor. This was covered with chain-mail, and in addition many devices were tried, such as roundels and the like, ending in the elaborate pauldron, cubitière, genouillière, etc.
2. n. An angular piece of iron or a kind of bracket fastened in the angles of a structure to give strength or stiffness. An angular piece of iron inserted in a boiler, tank, etc., where it changes from a cylindrical to a square form, as at the junction of the barrel and fire-box of a locomotive. A triangular piece of cloth inserted in a garment to strengthen or enlarge some part.
3. n. In heraldry, same as gore, 7.
4. To make with a gusset; insert a gusset into, as a garment.
5. n. In iron shipbuilding, a piece of plate of triangular form reinforcing on one side the junction of a part which meets another angularly, the gusset-plate being approximately normal to the line of the joint between the parts. See cut under bracket, 9 .

Wiktionary

1. n. A small piece of cloth inserted in a garment, for the purpose of strengthening some part or giving it a tapering enlargement.
2. n. A small piece of mail, providing some protection where two plates of armor are joined, usually at the elbows, under the shoulders, and behind the knees.
3. n. machinery 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.
4. n. heraldry An abatement or mark of dishonor in a coat of arms, resembling a gusset.
5. n. roofing A large flat metal piece wider than the valley to help prevent build-up at the base of the valley, either from debris or ice dam formations.

GNU Webster's 1913

1. n. A small piece of cloth inserted in a garment, for the purpose of strengthening some part or giving it a tapering enlargement.
2. n. Anything resembling a gusset in a garment.
3. n. (Armor) A small piece of chain mail at the openings of the joints beneath the arms.
4. n. (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.
5. n. (Her.) An abatement or mark of dishonor in a coat of arms, resembling a gusset.

WordNet 3.0

1. n. a piece of chain mail covering a place unprotected by armor plate
2. n. a piece of material used to strengthen or enlarge a garment
3. n. a metal plate used to strengthen a joist