piracy

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Robbery or other serious acts of violence committed at sea.
• noun The hijacking of an airplane.
• noun Copyright or patent infringement.
• noun The illegal interception or use of radio or television signals.
• noun An instance of piracy.

from The Century Dictionary.

• noun 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.
• noun Robbery upon the sea; robbery by pirates; the practice of robbing on the high seas.
• noun Literary theft; any unauthorized appropriation of the mental or artistic conceptions or productions of another; specifically, an infringement of the law of copyright.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act or crime of a pirate.
• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun 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
• noun the act of plagiarizing; taking someone's words or ideas as if they were your own