Definition of "Erse"

Two points which appeal to the writer are that the stations of origin and of destination are printed (in Erse and English) once only and then are summarised at the foot, [...]. [...] Clar Chloinne Mhuiris is the Erse original of Claremorris, and Dublin appears as Baile Atha Cliath.

1940 May, G. W. J. Potter, “Tickets of the Great Southern Railways”, in Railway Magazine, page 292

Now he's just sung in his mother tongue, the ancient Irish Erse, and cleared the pub completely by the forty-second verse!

1993, “Plastic Paddy”, in Mirrors‎, performed by Eric Bogle