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.
      [1913 Webster]

   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.
      [1913 Webster]
      [1913 Webster]

   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.
         [1913 Webster]

   3. "Sometimes used, in a quasi-figurative sense, of violation
      of copyright; but for this, infringement is the correct
      and preferable term." --Abbott.
      [1913 Webster]

WordNet (r) 3.0 (2006):

piracy
    n 1: hijacking on the high seas or in similar contexts; taking a
         ship or plane away from the control of those who are
         legally entitled to it; "air piracy" [syn: piracy,
         buccaneering]
    2: the act of plagiarizing; taking someone's words or ideas as
       if they were your own [syn: plagiarism, plagiarization,
       plagiarisation, piracy]

The Free On-line Dictionary of Computing (19 January 2023):

software piracy
piracy

    Making or distributing unauthorised copies of
   software, either for kudos or for profit.  See software
   theft.

   (2010-02-03)


The Devil's Dictionary (1881-1906):

PIRACY, n.  Commerce without its folly-swaddles, just as God made it.