'duarchic' originates from Modern English, specifically formed from the noun 'duarchy' + the adjectival suffix '-ic', where 'duarchy' ultimately draws on elements meaning 'two' and 'rule' (from Greek/Latin roots).

'duarchic' was formed in English from the noun 'duarchy' (English), which itself is modeled on Greek-derived formations such as 'diarchy' (Greek 'di-' meaning 'two' + 'arkhia' meaning 'rule'). Over time English speakers also analogized 'du-' (from Latin 'duo' 'two') with the Greek element to produce forms like 'duarchy' and then the adjective 'duarchic'.

Initially the roots referred specifically to 'two' + 'rule' (i.e., 'rule by two'); over time the modern adjective 'duarchic' came to mean 'relating to or characteristic of a duarchy' rather than describing the rulers themselves.