Hi, Zasmina - it isn't in Kennedy's book, Folksongs of Britain and Ireland. On this page (click), Aine Minogue has lyrics derived from the Kennedy/Gallagher recording, but I don't know how close it is to what Gallagher sang. Here's what Minogue has:

The Keening Song
(as sung by Aine Minogue)

S'airiu,
Agus a leanbh,
Cad a Dheanfaidh me,
Ta tu ar shiul uaim,
Agus airiu,
Agus anuiridh, nil duin ar bith agam,
'S airiu,
Agus me lion fein,
Da mbeithea go moch agam,
Agus och, och, airiu, gan thu, gan thu.

'Sairu, my child, what will I do, you're gone from me, and airiu, I've been left alone after a year, there is no one, and och, och airiu, without you, without you


Och and airiu - words of lamentation (the words were not important, merely the use of the singing voice as an emotional release in the face of sorrow)

Hope that helps.
-Joe Offer (e-mail sent)-