'armilla' originates from Latin, specifically the word 'armilla', where the root 'arm-' meant 'arm' or 'shoulder' and the diminutive suffix '-illa' meant 'little' or 'small'.

'armilla' continued in Medieval Latin and Old French (appearing as forms like 'armille') and entered Middle English in forms such as 'armill' or 'armilla', eventually surviving in modern English as 'armilla'.

Initially, it meant 'a small arm (or armlet)' in the literal, diminutive sense; over time it evolved into the specialized meanings of 'ornamental arm ring' and 'ceremonial/military armlet'.