The slab is irregularly shaped, just under a metre and a half long, and its surface holds an inscribed Latin cross worked in two-strand interlace with triquetra knots at each terminal. A triquetra is a three-cornered interlaced figure common in early medieval ecclesiastical carving, and here four of them anchor the arms of the cross with quiet precision. Above the crosshead, carved in Old Irish, are the words "or do moinach", a prayer for Moínach. Below the cross, in four lines of slightly larger text that are inverted relative to the cross above, a second inscription reads "or do moenach aite mog roin": a prayer for Móenach, tutor of Mogrón. The inversion is deliberate, oriented so that a reader standing at the foot of the slab could read the longer inscription the right way up, whilst the shorter dedication above the cross addressed someone approaching from the other direction.

The slab is thought to date from the later ninth or tenth century, placing it within a period of intense monastic activity on Scattery Island, whose community was associated with St Senan. Cross-slabs of this kind served as grave markers or memorial stones, and this example closely resembles a type documented at Clonmacnoise in County Offaly, one of the great centres of early Irish monasticism. The stylistic connection hints at either shared craftsmen or a common visual tradition circulating between major island and riverside monasteries of the period. The names preserved in the inscriptions, Móenach and Mogrón, are otherwise unattested in the historical record, but the word "aite", meaning foster-father or tutor, tells us something specific: Móenach held a recognised teaching role, and someone thought it worth recording. The slab sits approximately three metres west of St Senan's bed, a hollowed stone associated with the founder of the island's monastery, which gives the location a layered quality, with early medieval commemorations placed in deliberate proximity to an even older site of devotion.