Definition of "arrah"

"Whisht! whisht! Of what are ye thinking, ye silly gossoons? Will ye bring down the peace officers upon ye, and take out the bit o' the night in the prison, instead o' drinking me health, as ye may, and me helping to do that same? Arrah! Why should ye glower and snarl at each other, like a kennel o' mad puppies, when it's the brave frolic ye may have together?

1913, anonymous author, chapter VI, in Live to be Useful or, The Story of Annie Lee and Her Irish Nurse

"Such a nice clean corpse, did you ever see?"Arrah, Tim, mavourneen, why did you die?"

c. 1850s, Anonymous, Finnegan's Wake (folk song)