One who robs at sea or plunders the land from the sea without commission from a sovereign nation. A ship used for this purpose. One who preys on others; a plunderer. One who makes use of or reproduces the work of another without authorization. One that operates an unlicensed, illegal television or radio station. To attack and rob (a ship at sea). To take (something) by piracy. To make use of or reproduce (another's work) without authorization. To act as a pirate; practice piracy.