The Greek is παροικία which is used both for what is meant by the modern “diocese” and by the modern “parish.”  Of the sense of diocese instances are quoted among others in D.C.A. s.v. “Parish,” from Iren. ad Florin. apud Euseb. H.E. v. 20; and Alexand. Alexandrin. Ep. apud Theodoret, H.E. i. 3.