Pius XII Syllabification: (Pi·us XII)Pronunciation: /ˈpīəs/Definition of Pius XII (1876–1958), pope 1939–58; born Eugenio Pacelli. He upheld the neutrality of the Roman Catholic Church during World War II and was criticized after the war for failing to condemn Nazi atrocities. Pius XII in other Oxford dictionaries Definition of Pius XII in the British & World English dictionary