liner
n.— «The dealers search for coins that are the “sliders,” or the “liners,” as they are called, the ones that might glint in such a way on a certain day to become a 65, instead of a 64, in the eye of the right coin grader. It’s not illegal, but sins have been committed in the name of grading arbitrage in the high-dollar, fast-paced rare coin world.» —“Coin fund profits for state hinged on graders’ opinions” by Christopher D. Kirkpatrick Toledo Blad (Ohio) May 30, 2005. (source: Double-Tongued Dictionary)