​SYNCELLUS, a hybrid word (Gr. σύν, Lat. cello),^[1] meaning literally “one who shares his cell with another.” In ecclesiastical usage it refers to the very early custom of a priest or deacon living continually with a bishop, propter testimonium ecclesiasticum; thus Leo III. speaks of Augustine as having been the syncellus of Gregory the Great. The term came into use in the Eastern Church, where the syncelli were the chaplains of metropolitans and patriarchs. At Constantinople they formed a corporation, and the protosyncellus took precedence of metropolitans and ranked next to the patriarch, to whose office he generally succeeded.