Whatever name or prayer surrounded those letters is gone, worn away or broken off at some point in the many centuries since an early medieval craftsman cut them into the face of a small slab roughly the size of a hardback book. At only 42 centimetres tall, it is the smallest of five cross-slabs mounted together on a display structure built along the line of the east gable of an old church, and that modesty of scale makes the survival of even this much seem quietly remarkable.

Cross-slabs are flat stones, typically associated with early Christian burial or commemoration in Ireland, incised with a cross and sometimes an inscription naming the person to be prayed for. This example retains the lower portion of a cross stem, its base ending in what is described as a decorated expanded terminal rendered in false relief, meaning the carved design gives an impression of raised work without being fully three-dimensional. The four surviving letters were noted by R. A. S. Macalister, whose two-volume corpus of early Irish inscriptions, published in 1949, remains a standard reference for this kind of material. Whether THIR formed part of a personal name, a Latin formula, or something else entirely, Macalister recorded without being able to fully resolve it. Four of the slab's companions survive alongside it, together forming a small concentrated group that hints at the significance the Ballynakill site once held as a place of Christian community and burial in the early medieval period.