One of the mysteries of the English language finally explained.
Definition of armilla in US English:
armilla
noun
1Astronomy= "armillary sphere".
2A stole worn by the British sovereign at his or her coronation.
3Chiefly Archaeology. An arm-ring or bracelet.
Origin
Early 17th century; earliest use found in Thomas Oliver (d. ?1610), mathematician and physician. From classical Latin armilla armband, bracelet, metal hoop, ring, washer, socket, in post-classical Latin also stole, armillary sphere from armus shoulder + -illa.