| Bestiary | A work describing animal species and providing their allegorical signification |
| Easter controversy | A disagreement within the early medieval Church on the correct dating of Easter |
| Echtrae (pl. echtrai) | Lit. “outing”; an Irish genre in which individuals undertake journeys to the otherworld |
| Grimm’s Law | A sound law explaining the divergence between Germanic and other Indo-European consonants, as in eat and edere, fish and piscis |
| Immram (pl. immrama) | Lit. “rowing about”; an Irish monastic genre in which individuals sail off and encouter otherworld islands |
| Papar | Irish priests; the term is often used to refer to ascetics inhabiting out-of-the way maritime locations |
| Pelagianism | The belief that individuals may overcome sin by the strength of their own will |
| Penitential | A tariff list matching specific sins to their respective compensations, by rank of sinner and wronged party |
| Peregrinatio (pro Christo/amore Dei) | A self-imposed exile in pursuit of personal salvation |
| Public penance | A non-repeatable, public penitential system for grave sins used up to the seventh century. Penitents were excluded from communion as well as from various functions and interactions. |
| Sacrament of penance | A repeatable, private penitential system developed in the eleventh century. The processes of contrition, confession, satisfaction, and absolution can absolve any sinner of most sins. |
| Synod | A council of bishops; in British and Irish tradition, attended also by abbots and scholars |
| Tariff penance | A repeatable, private penitential system with fixed tariffs based on the nature of the sin, the rank of the sinner, and the rank of the wronged party. Originating in the British/Irish Churches, it became Catholic practice in the seventh century. |
| Verner’s Law | A modification to Grimm’s Law explaining some of the differences between Indo-European and Germanic consonants by the fact that the former used free stress, the latter root stress (i.e. fixed, initial stress) |