Source : Webster's Revised Unabridged Dictionary (1913)

Exarch \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.

Source : WordNet®

exarch
     n 1: a bishop in one of several Eastern Orthodox churches in
          North America
     2: a bishop in eastern Christendom who holds a place below a
        patriarch but above a metropolitan
     3: a viceroy who governed a large province in the Roman Empire