Green’s Dictionary of Slang

melia murder! excl.

also melia murdher! melia murther! millia...!
[Irish míle murdar, lit. ‘a thousand murders’, thus ‘horror of horrors!’]

(Irish) a general excl. of surprise, horror, regret.

[Ire]S. Lover Legends and Stories 168: ‘Oh then millia murther!’ says Paddy, ‘what’ll become of me at all.’.
[Ire] ‘A Letter [...] From Peter Strongbow etc.’ Dublin Comic Songster 310: Och, millia murther!
[UK]Greenwood A Little Ragamuffin 211: Melia murther! but it does the heart of an Irishman good to hear that swate song.
[Ire]L. Doyle Ballygullion (1927) 81: Michael in the middle av thim, an’ the wimmen hanging round, pullin’ the skirts av the men’s coats, an’ cryin’ melia murdher.
Ottumwa Tri-Weekly (IA) 27 Aug. 5/1: Millia murdher, the Omadhaun’s makin’ straight for the fairies’ bush.
[Ire]‘Flann O’Brien’ ‘Natotion’ in Hair of the Dogma (1989) 75: But there was sacred holy melia murder about it afterwards.