Ex"arch (?), n. [L. exarchus, Gr. &?; &?; commander; &?;,&?;, out + &?; to lead, rule: cf. F. exarque.] A viceroy; in Ravenna, the title of the viceroys of the Byzantine emperors; in the Eastern Church, the superior over several monasteries; in the modern Greek Church, a deputy of the patriarch , who visits the clergy, investigates ecclesiastical cases, etc.