If this debate is still going on, your man who said "Cúilfhionn" is right, "fair back", i.e. golden hair going down past the shoulders.

The only snippet I've got is the first verse, which is:

An bhfaca tú mo chúilfhionn,
Is é ag siúl thar na bhonntaibh?
Is é mo chroí gheal,
Mo réalt bhreá na maidine,
Mo chúilfhionn,
Ar fháinne gheal an lae.

Translated into Britspeak,

Have you seen my fair-backed one,
And he walking over the hills?
He's my fair heart,
My bright star of the morning,
My fair-backed one,
At the dawning of the day.

The rest of it would be appreciated.