Argues that boíthi replaced a morphologically ambiguous 3rd sg. pret. of the substantive verb *boí (< InsC *bowe + en), which may survive as the anomalous 3rd sg. pret. of the copula boí found in some passages of Amra Choluim Cille: §25 boe seim sáth ‘there was to him slender food’ (as ed. by W. Stokes in RC 20.168 [Best¹, p. 237]).