Isabel f. Old Provençal Elisabel 'Elizabeth'.
The name of a 12th C queen of France, a 12th-13th C queen of Jerusalem, a 13th C French saint, a 13th C queen of Navarre, a 13th C queen consort of Aragon, a 13th C queen consort of France, a 13th C queen consort of England, a 13th C queen of Jerusalem, a 13th C Holy Roman empress, a 13th c queen of Armenia, two 13th C queens of Cyprus, a 13th C Hungarian saint, two 14th C queens consort of England, a 14th C queen consort of Germany, a 14th C queen consort of Portugal and saint, a 14th-15th C queen consort of Castile, Leon, and Aragon, a 14th-15th C queen consort of France, a 15th C queen consort of Portugal, a 15th C queen consort of Castile and Leon, a 16th C queen consort of Sweden, Denmark, and Norway, a 16th C queen consort of Hungary, and a 16th C Holy Roman empress and queen of Spain and Italy.
Though in origin a form of Elizabeth, and sometimes even by the 17th C still used as a pet name of it in England, it very quickly became considered a distinct name.