The Oxford dictionary of opera1992

Over 4,500 entries on individual composers; operatic works; principal operatic roles; well-known arias, choruses, scenes, and interludes; sources of ideas for operas; details of librettists and their sources; singers, conductors, producers, directors, designers, and entrepreneurs; histories of opera-houses, companies, institutions, and festivals; history of opera in individual countries; those whose thought influenced opera; and specialized terms.