a group of British spies (= people employed to find out secret information) who gave British secrets to the Soviet Union. They were at Cambridge University together in the 1930s, and believed that Communism was the only way of fighting Fascism. People first knew about the group when two of them, Guy Burgess and Donald Maclean, went to live in the Soviet Union in 1951. A third man, Kim Philby, joined them in 1963, and in 1979 the fourth man was named as Anthony Blunt. John Cairncross was named as a fifth member of the group in 1991.