Swaybacked describes a back that curves downward in the middle, so the middle sags and the two ends look higher. Picture a very old horse: the belly hangs, the spine dips, the shoulders and hips stand up at either end. That dip is what the word names. It started with horses and is still most at home there, where it usually means the animal is old, or has carried too much weight for too long. It is used of people too — a swaybacked posture, where the lower back curves in sharply and the stomach pushes forward. Doctors have their own name for this, lordosis, but ordinary people say swaybacked. And it travels to things that are not alive at all. An old barn roof, a shelf loaded with too many books, a bed that has been slept in for thirty years — all swaybacked. Anything long that has given way in the middle under years of weight. The feeling of the word is gentle sadness. It says: this has been used a long time, and it is tired. You would not describe something new and strong as swaybacked, even if it happened to curve that way. You will see it written swaybacked, sway-backed, or as the noun swayback.

（背、屋頂、床、書架）中間下凹的、凹陷下垂的。原本形容老馬的背下塌，也可形容人的下背過度前凹（醫學上叫脊椎前凸），或用久了中間垮下去的屋頂、床墊。