Bullaun stones are boulders or slabs worked with one or more cup-shaped depressions, most likely ground out by hand over generations. They are found throughout Ireland, often near early ecclesiastical sites, and their precise purpose remains debated, with suggestions ranging from liturgical use to the grinding of pigments or medicines. The name Cill Maoilchéadair, containing the Irish word cill for church or cell, points to exactly the kind of early Christian context in which bullauns most commonly appear.

The stone itself is substantial: 1.8 metres long, 1.2 metres wide, and only about 0.2 metres thick, giving it the character of a large, worked slab rather than a rounded boulder. On one face there is a circular depression measuring 0.38 metres across and 0.08 metres deep, clearly artificial in origin. A longer hollow beside it may, according to the 1986 Corca Dhuibhne archaeological survey compiled by J. Cuppage, be entirely natural, which is a useful reminder that not every mark on an ancient stone carries meaning. Since its discovery the stone has been set standing against the new wall on the western side of the roadway, which preserves it in place but shifts it into a slightly awkward posture: a flat-lying ritual or working stone now displayed vertically, like a book shelved on its spine.