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 (30 December 2018):

software piracy
piracy

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

   (2010-02-03)


Bouvier's Law Dictionary, Revised 6th Ed (1856):

PIRACY, crim. law. A robbery or forcible depreciation on the high seas,
without lawful authority, done animo furandi, in the spirit and intention of
universal hostility. 5 Wheat. 153, 163; 3 Wheat. 610; 3 Wash. C. C. R. 209.
This is the definition of this offence by the law of nations. 1 Kent, Com.
183. The word is derived from peira deceptio, deceit or deception: or from
peiron wandering up and down, and resting in no place, but coasting hither
and thither to do mischief. Ridley's View, Part 2, c. 1, s. 3.
     2. Congress may define and punish piracies and felonies on the high
seas, and offences against the law of nations. Const. U. S. Art. 1, s. 7, n.
10; 5 Wheat. 184, 153, 76; 3 Wheat. 336. In pursuance of the authority thus
given by the constitution, it was declared by the act of congress of April
30, 1790, s. 8, 1 Story's Laws U. S. 84, that murder or robbery committed on
the high seas, or in any river, haven, or bay, out of the jurisdiction of
any particular state, or any offence, which, if committed within the body of
a county, would, by the laws of the United States, be punishable with death,
should be adjudged to be piracy and felony, and punishable with death. It
was further declared, that if any captain or manner should piratically and
feloniously run away with a vessel, or any goods or merchandise of the value
of fifty dollars; or should yield up such vessel voluntarily to pirates; or
if any seaman should forcible endeavor to hinder his commander from
defending the ship or goods committed to his trust, or should make revolt in
the ship; every such offender should be adjudged a pirate and felon, and be
punishable with death. Accessaries before the fact are punishable as the
principal; those after the fact with fine and imprisonment.
     3. By a subsequent act, passed March 3, 1819, 3 Story, 1739, made
perpetual by the act of May 15, 1820, 1 Story, 1798, congress declared, that
if any person upon the high seas, should commit the crime of piracy as
defined by the law of nations, he should, on conviction, suffer death.
     4. And again by the act of May 15, 1820, s. 3, 1 Story, 1798, congress
declared that if any person should, upon the high seas, or in any open
roadstead, or in any haven, basin or bay, or in any river where the sea ebbs
and flows, commit the crime of robbery in or upon any ship or vessel, or
upon any of the ship's company of any ship or vessel, or the lading thereof,
such person should be adjudged to be a pirate, and suffer death. And if any
person engaged in any piratical cruise or enterprize, or being of the crew
or ship's company of any piratical ship or vessel, should land from such
ship or vessel, and, on shore; should commit robbery, such person should be
adjudged a pirate and suffer death. Provided that the state in which the
offence may have been committed should not be deprived of its jurisdiction
over the same, when committed within the body of a county, and that the
courts of the United States should have no jurisdiction to try such
offenders, after conviction or acquittal, for the same offence, in a state
court. The 4th and 5th sections of the last mentioned act declare persons
engaged in the slave trade, or in forcibly detaining a free negro or mulatto
and carrying him in any ship or vessel into slavery, piracy, punishable with
death. Vide 1 Kent, Com. 183; Beaussant, Code Maritime, t. 1, p. 244;
Dalloz, Diet. Supp. h.t.; Dougl. 613; Park's Ins. Index, h.t. Bac. Ab. h.t.;
16 Vin. Ab. 346; Ayl. Pand. 42 11 Wheat. R. 39; 1 Gall. R. 247; Id. 524 3 W.
C. C. R. 209, 240; 1 Pet. C. C. R. 118, 121.



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PIRACY, torts. By piracy is understood the plagiarisms of a book, engraving
or other work, for which a copyright has been taken out.
     2. When a piracy has been made of such a work, an injunction will be
granted. 5 Ves. 709; 4 Ves. 681; 12 Ves. 270. Vide copyright.



The Devil's Dictionary (1881-1906):

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