The Collaborative International Dictionary of English v.0.48:

Piracy \Pi"ra*cy\, n.; pl. Piracies. [Cf. LL. piratia, Gr. ?.
   See Pirate.]
   1. The act or crime of a pirate.
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   2. (Common Law) Robbery on the high seas; the taking of
      property from others on the open sea by open violence;
      without lawful authority, and with intent to steal; -- a
      crime answering to robbery on land.
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   Note: By statute law several other offenses committed on the
         seas (as trading with known pirates, or engaging in the
         slave trade) have been made piracy.
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   3. "Sometimes used, in a quasi-figurative sense, of violation
      of copyright; but for this, infringement is the correct
      and preferable term." --Abbott.
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