'duumviral' originates from Latin, specifically the adjective 'duumviralis', derived from 'duumvir' (from 'duo' meaning 'two' + 'vir' meaning 'man'), with the adjectival suffix '-alis' forming 'relating to a duumvir'.

'duumviral' changed from the Latin adjective 'duumviralis' and the noun 'duumvir' into Late Latin/Medieval usage and eventually entered English as the adjective 'duumviral' (by formation on the model of Latin-to-English adjectival adaptation).

Initially, it referred specifically to things 'pertaining to a duumvir (two-man magistracy)' in Roman contexts; over time it retained that primary sense and has come to be used more generally for 'relating to a joint rule by two'.