means A dramatic work in which the story is sung rather than spoken, performed by singers with orchestral accompaniment, often on a grand and theatrical scale.

from Straight from Italian opera, meaning 'a work' or 'labor,' which itself comes from Latin opera, the plural of opus — 'work' — the same root that gives us 'operate' and 'opus.' The full original phrase was opera in musica, 'a work in music,' and over time the music part fell away while the work part stayed to sing for three hours. So at its heart, opera literally just means 'works' — fittingly, since it bundles music, drama, poetry, and scenery into one enormous labor.