1560s in medical use, "ring-like area or space," from a Medieval Latin misspelling of Latin anulus "little ring, finger ring," a diminutive of anus "ring" (see anus).
Entries linking to annulus
anus n.
"inferior opening of the alimentary canal," 1650s, from Old French anus, from Latin anus "ring, anus," from PIE root *āno- "ring." So called for its shape; compare Greek daktylios "anus," literally "ring (for the finger)," from daktylos "finger."