EYESTONE
Etymology
Noun
eyestone (plural eyestones)
A small, lenticular, calcareous body, especially an operculum of a small shell of the family Tubinidae, used to remove a foreign substance from the eye.
(mineral) Eye agate.
Source: Wiktionary
Eye"stone`, n.
1. A small, lenticular, calcareous body, esp. an operculum of a small
shell of the family Tubinid, used to remove a foreign sub stance from
the eye. It is rut into the inner corner of the eye under the lid,
and allowed to work its way out at the outer corner, bringing with
the substance.
2. (Min.)
Definition: Eye agate. See under Eye.
Source: Webster’s Unabridged Dictionary 1913 Edition