OPERA n.
ung, consisting of recitative, arials, choruses, duets, trios, etc., with orchestral accompaniment, preludes, and interludes, together with appropriate costumes, scenery, and action; a lyric drama.
ORATORIO n.
to music, in recitative, arias, grand choruses, etc., to be sung with an orchestral accompaniment, but without action, scenery, or costume, although the oratorio grew out of the Mysteries and the Miracle and Passion plays, which were acted.
ORCHESTRA n.
band suitable for the performance of symphonies, overtures, etc., as well as for the accompaniment of operas, oratorios, cantatas, masses, and the like, or of vocal and instrumental solos.