piracy

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Robbery committed at sea.
2. n. A similar act of robbery, as the hijacking of an airplane.
3. n. The unauthorized use or reproduction of copyrighted or patented material: software piracy.
4. n. The operation of an unlicensed, illegal radio or television station.

Century Dictionary and Cyclopedia

1. n. Robbery upon the sea; robbery by pirates; the practice of robbing on the high seas. Specifically, in the law of nations, the crime of depredations or wilful and aggressive destruction of life or property committed on the seas by persons having no commission or authority from any established state. As commonly used it implies something more than a simple theft with violence at sea, and includes something of the idea of general hostility to law. According to the opinion of some, it implies only unlawful interference with a vessel; according to others, it includes also depredations on the coast by a force landing from the sea. The slave-trade was declared piracy by statute in the United States May 15, 1820, by Great Britain in 1824, and since the treaty of 1841 by Austria, Prussia, and Russia.
2. n. Literary theft; any unauthorized appropriation of the mental or artistic conceptions or productions of another; specifically, an infringement of the law of copyright.
3. n. In geology, that process whereby, because of a higher natural gradient, and therefore more efficient eroding power, one stream cuts back a divide and taps off the head-waters or a tributary of another stream. The captured stream usually turns a sharp angle into its new course and leaves a wind-gap where it formerly flowed. Also called stream-piracy.

Wiktionary

1. n. nautical Robbery at sea, a violation of international law; taking a ship away from the control of those who are legally entitled to it.
2. n. A similar violation of international law, such as hijacking of an aircraft.
3. n. The unauthorized duplication of goods protected by intellectual property law (e.g. copying software unlawfully).
4. n. The operation of an unlicensed radio or television station.

GNU Webster's 1913

1. n. The act or crime of a pirate.
2. n. (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.

WordNet 3.0

1. n. 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
2. n. the act of plagiarizing; taking someone's words or ideas as if they were your own