Three medieval Irish manuscripts, two of which are almost entirely medical in content, preserve a hitherto unpublished passage of commentary in Irish on the meaning of the Latin word magister (‘teacher’ or ‘master’). The text in question consists chiefly of a series of expositions on the eight letters of the term magister that serve to highlight various attributes associated with an individual bearing that title. Each explanation cites a different Latin word, the initial letter of which corresponds to one of the letters in the word magister. These Latin terms are then translated into Irish, and followed in turn by succinct interpretations of how each concept relates to the function and duties of a magister. The present contribution offers an annotated edition and translation of this passage, and attempts to situate its contents within the wider context of medieval Irish intellectual culture