n. 1. A small, lenticular, calcareous body, esp. an operculum of a small marine shell of the family Turbinidæ, used to remove a foreign substance from the eye. It is put into the inner corner of the eye under the lid, and allowed to work its way out at the outer corner, bringing with it the substance. [ 1913 Webster ]

2. (Min.) Eye agate. See under Eye. [ 1913 Webster ]

n. (Arch.) The central or topmost stone of an arch. This in some styles is made different in size from the other voussoirs, or projects, or is decorated with carving. See Illust. of Arch. [ 1913 Webster ]

. Pennsylvania; -- a nickname alluding to its having been the central one of the 13 original United States, at the time of formation of the Constitution. [ Webster 1913 Suppl. ]