It is easy to overlook, being neither tall nor ornate, but it is a font, a vessel intended for holy water, and its placement at this threshold rather than on a plinth or ledge gives it an quietly functional quality that most ecclesiastical stonework has long since lost.

The block measures roughly 36 by 34 centimetres and stands just 30 centimetres high, with a circular basin carved into its upper face, about 25 centimetres across and 18 centimetres deep. The material is plain limestone, undecorated, and one corner has broken away at some point in the centuries since the priory was in use. It belongs to the Augustinian religious house on the island, a community of canons regular who followed the Rule of St Augustine, a form of monastic life that became widespread in Ireland from the twelfth century onwards. The font's position in the south-western doorway connecting the church to the cloister suggests it served a practical, daily role in the devotional routine of that community, marking the passage between spaces with a small act of blessing or purification.

Canon Island is accessible only by water, which means the font has remained largely undisturbed, sitting in the same doorway threshold where it was apparently always intended to be. The ruined priory around it is the more visually prominent structure, but the stone basin on the floor rewards a closer look, not least because so few fonts of this type survive in situ rather than having been moved into storage or lost entirely.