OPERA, n. A play representing life in another world, whose inhabitants have no speech but song, no motions but gestures and no postures but attitudes. All acting is simulation, and the word simulation is from simia, an ape; but in opera the actor takes for his model Simia audibilis (or Pithecanthropos stentor)--the ape that howls.
The actor apes a man--at least in shape;
The opera performer apes an ape.
2009 Update: A coincidence of sheet music with a libretto, typically tragic. The term derives from the Latin plural of OPUS, meaning "works" or is, perhaps, a durable misprint of "ONERA."