[Ruaidhri, son of Thomas Mag Uidhir, namely, son of the king of Fir-Manach, died this year (that is, on the 4th of the Ides 10th of February) of a fit.]
R: Ruaidhri Blind -eye, namely, son of Thomas Mag Uidhir (that is, king of Fir-Manach was Thomas) died. (His death resulted from a fit.)