The Celtic languages (CL) belong to the group of Centum languages within the Indo-European languages. The hypothesis that the preliminary phases of the Italic and the Celtic language branch form a unit was long disputed. For morphological reasons in particular (common innovations exclusive to Celtic and Italic), early Italic-Celtic language unity is, however, probable [1]. The CL are usually subdivided in two regards.
a) Purely geographical classification as ‘mainland Celtic’ and ‘island Celtic’ without reference to differences or common fe…