bullion
A figure or ornament of concentric bands. 2. A round or oval aperture, open louvered, or glazed; an oculus or oeil-de-boeuf. 3. The enclosure of such an aperture, a double-arched frame with two or four key voussoirs. 4. A glass disk formed with a raised center. Same as bull’s eye. (Harris, 1977)
bull's eye