Amalgaid (d. 1049), abbot of Armagh, son of Abbot Máel-Muire, belonged to the ecclesiastical lineage of Clann Sínaig, and heads the genealogy of his line in Rawlinson B. 502, being eighth in descent from the eponymous Sínach. The lineage was a discard segment of the Uí Echdach dynasty, which provided the local kings of Airthir (which left its name on the baronies of Upper and Lower Orior, east Co. Armagh). Clann Sínaig, like other ecclesiastical lineages of the pre-reform era, filled church offices on a hereditary basis with clerics who were not necessarily in major orders.
Amalgaid directly succeeded his father Máel-Muire (qv) (d. 1020), who was abbot for twenty-two years. Máel-Muire's father, Eochaid son of Cellach (d. 1004), had been abbot of Clonfeakle and airchinnech (superior) of the les oígedh (guesthouse) at Armagh. After his institution as abbot, Amalgaid undertook a visitation in Munster, on which occasion an ecclesiastical tax was levied on the province. His death at the beginning of July 1049 is recorded as follows: ‘Amalgaid, successor of Patrick [qv], having completed twenty-nine years as superior, rested penitently in Christ’ (AU); a poem lamenting his passing is appended. He was succeeded in the abbacy by his brother Dub-dá-Leithe (qv), who had been fer léigind (lector or chief scholar) of Armagh since 1046. Two sons of Amalgaid later served as abbots: Máel-Ísu (1064–91) and Domnall (qv) (1091–1105).