N-COUNT
（按創作的先后次序排列的某一作曲家的）編號作品（縮略形式為op.）
An opus is a piece of classical music by a particular composer. Opus is usually followed by a number which indicates at what point the piece was written. The abbreviation op. is also used.
例句
...Beethoven's Piano Sonata in E minor, Opus 90.
貝多芬的第90號E小調鋼琴奏鳴曲