A smooth, oval-shaped stone or pellet made of polished wood, glass, or other material, placed in the eye to remove dirt or foreign particles.
From 'eye' + 'stone.' A folk remedy term that emerged in the 19th century, though the practice of using smooth objects to clean eyes is much older.
Before eyedrops and saline solutions, eyestones were a genuine medical tool—you'd put one in your eye and the irritation would cause your eye to produce tears that'd wash out debris, showing how our bodies can be coaxed into healing themselves.
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