the world > animals > animal body > general parts > body and limbs > [adjective] > relating to the back > sway-backed (3)
Of a horse: Having a depression in the spinal column, caused by strain. Also back-swayed, sway-backed, adj. Obsolete.
Of an animal, esp. a horse: Having a downward curvature of the spinal column; strained in the back, as by overwork. Also transferred.