Davod is said to have written a grammar of the Welsh language, published in 1856 by the Welsh Manuscripts Society, with an English translation and notes by the Rev. John Williams ab Ithel. The introduction states that Edeyrn "performed it by command and at the desire of these three lords paramount, namely, Llewelyn, son of Gruffydd, prince of Aberffraw, and king of all Wales; Rhys Fychan, lord of Dinefwr and Ystrad Towy; and Morgan Fychan, lord of the territory between Nedd and Afan and Cilfai, and lord paramount of Morganwg."
The same introduction, which can hardly in propriety be Edeyrn's work, speaks of Edeyrn's "acute and profound genius, reflection, various acquirements, memory, and retention." He compiled it "from the record which Einiawn the priest had formed." It includes not only "the Cymric letters and parts of speech," but "the metres of vocal song." The version published is said to have been "copied from a transcript of Mr. Lewis Richards of Darowen, Montgomeryshire, dated 1821, by the Rev. W. J. Rees of Cascob, Radnorshire, 1832," and we are informed that "Mr. Richards appears to have taken his copy from a manuscript of Iolo Morganwg."