Complex sentence: In English usage, besides the word "opus", the word "opera" occasionally was used to identify a musical work; yet, in contemporary usage, the word "opera" denotes the dramatic musical genre of opera, which was developed in Italy.
Split into simpler sentences: In English usage, besides the word "opus", the word "opera" occasionally was used to identify a musical work. In contemporary usage, however, the word "opera" specifically denotes the dramatic musical genre of opera, which was developed in Italy.