submarine patent
 n.— «Occasionally, patents take a decade or two to be granted because they are held up in appeals and amendments in the Patent Office. When this happens under the existing system, an inventor can obtain a 17-year monopoly on an invention made long ago and demand payments from companies that have long been using the technology on the assumption that it was not protected by patents. Because these patents remain hidden for a long time and suddenly surface, they have been called “submarine patents.”» —“U.S. Agress to Alter Patents’ Period of Coverage” by Andrew Pollack in Tokyo New York Times Jan. 24, 1994. (source: Double-Tongued Dictionary)