The leg of a sheep used as food.
1That resembles a leg of mutton in shape or appearance.
2Designating a sleeve which is full and loose around the upper arm but tight-fitting on the forearm and wrist. Chiefly in "leg-of-mutton sleeve".
Designating a type of triangular sail, especially a mainsail, now typically one used on a small craft where the sprit or boom stretches the clew of the sail without being fixed to the foot, and the foot of the sail normally extends below the boom. Chiefly in "leg-of-mutton sail" or "leg-of-mutton rig". Also called mutton-ham sail, shoulder of mutton sail, shoulder of mutton rig.
Late 16th century; earliest use found in Charges Dinner Lord Leiyster at Oxford. From leg + of + mutton.