Noun
A cardinal of the Roman Catholic Church who is bishop of one of the cardinal ("hinge") dioceses of the Province of Rome.
(more loosely) A cardinal who is a bishop anywhere.
Source: en.wiktionary.orgThe cardinal bishop of Sabina was finally elected Pope Celestine IV by the required two-thirds majority, seven cardinals out of ten, only on 25 October 1241. Source: Internet
Since then, cardinals have been advanced to cardinal bishop exclusively by papal appointment. Source: Internet