What is the meaning of Opera?

A drama, either tragic or comic, of which music forms an essential part; a drama wholly or mostly sung, consisting of recitative, arials, choruses, duets, trios, etc., with orchestral accompaniment, preludes, and interludes, together with appropriate costumes, scenery, and action; a lyric drama.

Source: Webster’s Revised Unabridged Dictionary (1913), via OPTED