acetabulum

Roman kitchens kept a small ceramic vessel for vinegar — the condiment Romans used as commonly as salt. They called it the acetabulum, built from acetum (vinegar, itself from acere, to be sour) and -bulum, a Latin suffix indicating a vessel or instrument. The word appears in Plautus in the second century BCE and in Cato's agricultural writings. At its most literal, it was the cup set on the table beside the bread.

Roman physicians noticed something in the human skeleton that looked exactly like that vinegar cup: the deep hemispherical cavity in the pelvis where the head of the femur sits. Celsus, writing in the first century CE, used acetabulum to name this socket in his encyclopedic medical text De Medicina. The naming was precise. The socket is genuinely cup-shaped, roughly fifty millimeters across, and the femoral head fits into it the way a ladle fits a bowl.

Medieval anatomists working from Arabic translations of Galen and Celsus preserved the term intact. Andreas Vesalius, in his 1543 De Humani Corporis Fabrica, illustrated the acetabulum in meticulous detail and kept the Latin name. The word traveled from manuscript to printed book to dissection theater without losing its original meaning.

Today the acetabulum appears in orthopedic surgery more often than in any kitchen. Hip replacement surgery, one of the most common procedures performed on people over sixty, involves fitting a prosthetic cup precisely into the acetabulum. The vinegar vessel is now titanium.