The New Grove Dictionary of Opera is an encyclopedia of opera, considered to be one of the best general reference sources on the subject. It is the largest work on opera in English, and in its printed form, amounts to 5,448 pages in four volumes.
First published in 1992 by Macmillan Reference, London, it was edited by Stanley Sadie with contributions from over 1,300 scholars. There are 11,000 articles in total, covering over 2,900 composers and 1800 operas. Appendices including an index of role names and an index of incipits of arias, ensembles, and opera pieces.
The dictionary is available online, together with The New Grove Dictionary of Music and Musicians.(Wikipedia)