'armillary' originates from Latin, specifically the word 'armillāris', where 'armilla' meant 'bracelet' or 'armlet'.

'armillāris' in Late Latin (meaning 'of a bracelet') was extended in Medieval and Renaissance Latin to describe ring-like structures; this sense led to the Late Latin/Modern Latin use for astronomical ring-models and then into English as 'armillary'.

Initially it meant 'of or relating to a bracelet', but over time it evolved into its current meaning of 'relating to an armillary sphere' or 'a ringed model representing the heavens'.