Lewis & Short

dŭumvĭrātus (also DVOMVIR., Inscr. Momms. 2378), ūs, m. [duumviri], the office of a duumvir, duumvirate, Plin. Ep. 4, 22, 1; Dig. 50, 3, 1; Inscr. Orell. 3817 (Momms. 2096; 4059).