palm shiner noun in gambling, an object that reflects the image of cards, small enough to be held in the user’s hand US
The other was a “palm shiner,” which he used when it wasn’t his deal. It was a tiny, upside-down periscope. He could palm it, or hold it cupped in his hand on the green felt table, positioned so he could look down through the space between his fingers. — Stephen J. Cannell, KingCon, p. 2, 1997