The four letter answer to the crossword is 'Pius'. Pius was the name of three 20th-century Popes. The first was Pope Pius X, who reigned from 1903 to 1914. He was known for his conservative views and his efforts to modernize the Catholic Church. The second was Pope Pius XI, who reigned from 1922 to 1939. He was a strong advocate for social justice and worked to improve relations between the Church and the Italian government. The third was Pope Pius XII, who reigned from 1939 to 1958. He was a vocal opponent of Nazi Germany and helped to save thousands of Jews during World War II.