Latin for 'I do not wish to be a bishop', a phrase traditionally uttered by someone elected bishop, to show they are not seeking the post for their own gain or glory. It may therefore be used by anyone reluctant to take up responsibility.
One example is an incident in 1114 when Henry I appointed Abbot Ernulf of Peterborough to be Bishop of Rochester (succeeding Bishop Ralph, who was promoted to the See of Canterbury). Ernulf steadfastly refused and was not to be persuaded, so King Henry ordered him to be dragged away and consecrated regardless. However, the tradition is much older than this.
See the Anglo-Saxon Chronicle at www.britannia.com/history/docs/1114-20.html