annulus

The story

1. Medieval Latin · learned borrowing fromānnulī
2. Proto-Indo-European · derived from*h₁eh₂-n-o-“ring”
3. Latin · derived fromānulus“ring, especially one worn on a finger”
4. Medieval Latin · learned borrowing fromānnulus
5. English todayannulus

Learned borrowing from Medieval Latin ānnulus, a misspelling of Latin ānulus (“ring, especially one worn on a finger”), from ānus (“ring”) (possibly from Proto-Indo-European *h₁eh₂-n-o- (“ring”), from an uncertain root) + -ulus (diminutive suffix). The plural form annuli is a learned borrowing from Medieval Latin ānnulī.