n. pl. pi·ra·cies
a. Robbery committed at sea.
b. A similar act of robbery, as the hijacking of an airplane.
2. The unauthorized use or reproduction of copyrighted or patented material: software piracy.
3. The operation of an unlicensed, illegal radio or television station.
[Medieval Latin piratia, from Late Greek peirateia, from Greek peirates, pirate; see pirate.]