The shortest and earliest version of the work is ascribed to Cormac mac Cuilennáin (d. 908), king-bishop of Munster.
In some cases, he attempts to give the etymology of the words, and in others he concentrates on an encyclopedic entry.
It is held to be the earliest vernacular dictionary in any of the non-classical languages of Europe.
[3][4] The work may have been included in the Saltair Chaisil ("Psalter of Cashel"), a now-lost manuscript compilation that is thought to have contained various genealogical and etiological lore relating to Munster.
The versions of Sanas Cormaic divide into two groups: the earliest and shortest version represented by Leabhar Breac and the fragment in MS Laud 610, and a longer one represented by the Yellow Book of Lecan, which underwent some expansion in the hands of later redactors.