vertebra

Borrowed from Latin vertebra, meaning "a joint," which comes from vertō, "to turn," plus -bra, a suffix used to name instruments or tools.

Because a backbone made of many small turning joints, rather than one solid bone, is what lets the body bend and twist, this idea of "turning" became the word for each individual bone in the spine.

It shares its root vertō, "to turn," with the very idea of turning itself, embedded right in its own instrumental ending -bra.