'armilla' originates from Latin, specifically the word 'armilla', a diminutive of 'armus', where 'armus' meant 'shoulder' or 'upper arm' (i.e., an arm-related part).

'armilla' passed through Classical and Medieval Latin largely unchanged and was borrowed into English (often in scholarly, archaeological, or antiquarian contexts) as 'armilla' with the Latin plural 'armillae' and the anglicized plural 'armillas'.

Initially it meant 'a small arm ornament' in Latin, and over time it retained that core sense while also coming to be used specifically for 'ceremonial or military bracelets' in historical descriptions.