'armilla' originates from Latin, specifically the word 'armilla', where the root 'arm-' (from 'armus') meant 'arm' or 'shoulder'.

'armilla' passed from Classical Latin into Medieval Latin and later entered English as a learned borrowing; the plural forms have included Latin 'armillae' and the Anglicized 'armillas'.

Initially, it meant 'a ring or band for the arm', and over time it has retained that basic meaning as 'bracelet' or 'armlet'.