This is a bullaun stone, a type of boulder or slab bearing one or more cup-shaped depressions that appear at early medieval ecclesiastical sites across Ireland. Their precise original function is debated; suggestions range from the practical, grinding grain or preparing pigments, to the ritual, collecting rainwater believed to carry curative or protective properties. Whatever their original purpose, they tend to linger at sacred sites long after the communities that made them have disappeared.

This particular example is roughly trapezoidal in shape, measuring 0.56 metres in length and between 0.33 and 0.47 metres in width. Placed slightly off-centre on its flat upper surface is an oval hollow, 0.41 metres long, 0.31 metres wide, and 0.09 metres deep. Teaghlach Éinne, the church it belongs to, is one of several early Christian remains clustered at Cill Éinne, the settlement on the eastern end of Inis Mór that takes its name from Saint Enda, the sixth-century monastic founder whose community here became one of the most influential in early Irish Christianity. A second bullaun stone sits on the opposite side of the same church, diagonally across from the doorway, making the pair an unusual feature within a site already layered with early medieval remains.