Source : Webster's Revised Unabridged Dictionary (1913)

Opus \O"pus\, n.; pl. {Opera}. [L. See {Opera}.]
   A work; specif. (Mus.), a musical composition.

   Note: Each composition, or set of pieces, as the composer may
         choose, is called an opus, and they are numbered in the
         order of their issue. (Often abbrev. to op.)

Source : WordNet®

opus
     n : a musical work that has been created; "the composition is
         written in four movements" [syn: {musical composition}, {composition},
          {piece}, {piece of music}]

Source : Free On-Line Dictionary of Computing

Opus
     
         A {Honeywell} {operating system} promised
        as a sop to customers after canning {Multics} in 1985.  Opus
        was to provide everything Multics had and more, plus total
        compatibility with the {Level 6}/{DPS6} operating system.
     
        "Opus" was a code name, the system was officially named VS3
        (short for HVS R3 or Honeywell Virtual System Release Three).
        It was to run on the {DPS6-plus} hardware known internally as
        the MRX and HRX, and be all things to all people.
     
        The hardware was a dud (though it did run the native DPS6
        software just fine), and the goal was, shall we say,
        ambitious.  The effort was cancelled by {Bull} in 1987, in
        favor of another project going on in France.