a bishop having jurisdiction over a diocese
"The diocesan bishop announced that all parishes within his territory must adhere to the new liturgical guidelines."
The bishop of a diocese.
"The diocesan visited each parish to ensure that all clergy were adhering to the new guidelines."
belonging to or governing a diocese
"The newly appointed bishop will oversee all diocesan schools in the region."
Pertaining to a diocese.
"The bishop addressed the entire diocesan council before announcing the new mission strategy for next year."