From Greek 'dioikesis' (administration) — a Roman district adopted by the Church for a bishop's territory.
A district under the pastoral care of a bishop in the Christian Church; an ecclesiastical administrative territory.
From Old French 'diocise,' from Late Latin 'diocēsis,' from Latin 'dioecēsis' (a governor's jurisdiction, an administrative district), from Greek 'dioikēsis' (διοίκησις), meaning administration, management, or a governed district. The Greek word derives from 'dioikein' (διοικεῖν), to manage or administer, composed of 'dia-' (through, thoroughly) and 'oikein' (to manage a household), from 'oikos' (house). The Christian Church adopted the Roman administrative term for its own territorial divisions. Key roots: dia- (διά) (Greek: "through, thoroughly"), oikos (οἶκος) (Greek: "house
The Greek root 'oikos' (house) in 'diocese' is the same root that appears in 'economy' (house management), 'ecology' (study of the household of nature), and 'ecumenical' (of the whole inhabited world). A bishop managing a diocese is, etymologically, doing the same thing as an economist — running a household, just on a larger scale.