Coelchu, also COLGA, COLCU (Lat. Coleus), a distinguished Abbot of the School of Clonmacnoise in Ireland, who flourished during the latter half of the eighth century. He had been a student of this school, and had devoted himself especially to the study of St. Paul, whom he looked upon as his special patron. Coelchu was remarkable for his learning, and was surnamed the Scribe, and also the Wise. Colgan (Acta Sanctorum Hiberni) mentions one tract from the pen of Coelchu which was then extant, and which was entirely of a devotional character. He is generally assumed to be the person with whom Alcuin apparently had some correspondence. A letter of Alcuin's to him has been published by Ussher (Sylloge, Ep. xviii) and republished by Colgan. It is headed "Albini Magistri ad Colcum lectorem in Scotia. Benedicto magistro et pio patri Colcu Alcuinus humilis levita salutem". There can hardly be any doubt that the Colcu spoken of was the Abbot of Clonmacnoise, and that the writer of the letter was Alcuin, not Albin the companion of Clement, though there is no reason for concluding from the style of the address that Alcuin had ever been a student of Coelchu's at Clonmacnoise. In this letter Alcuin gives Coelchu an account of the state of religion on the Continent, mentions Joseph, one of Coelchu's pupils then in France, speaks of disputes between King Charles and Offa of Mercia, on account of which he himself was likely to be sent as negotiator into England. This clearly proves that the letter was written shortly before 790. He sends Coelchu presents of money from King Charles and from himself for the monastery of Clonmacnoise and for other monks in Ireland, and asks their prayers for himself and the king. There is another reference to Coelchu in Alcuin's letter to Joseph, mentioned already in the letter to Coelchu. Though Coelchu was spoken of as the Scribe or Doctor of all the Irish, none of his writings have come down to us.