"Glè mhath, a Nèill."
Translation:Very good, Niall.
Is this just an 'irregular' vocative because you want to avoid vowel soup? You don't lenite because the first letter is N but you need to slenderise and would normally add an i before the 'll'. But that would give you 'Niaill' so it gets pruned and turned into Neill? Or have I made that up?!