"The definitive record of the English language." Including 600,000 words from over a millennium, the OED not only defines, but provides historical context for, English words from the everyday to the arcane.
Composer, performer and librettist biographies, encyclopedic coverage of music genre and form, works lists. Combines the New Grove Dictionary of Music and Musicians, the New Grove Dictionary of Opera, the New Grove Dictionary of Jazz, the Oxford Dictionary of Music, and the Oxford Companion to Music. Your professor told you to "use Grove". This is it.