1841, Edward FitzGerald, letter to W. F. Pollock dated 10 February, 1841, in The Variorum and Definitive Edition of the Poetical and Prose Writings of Edward FitzGerald, Volume 7, p. 22,
Luckily for you, my farming is a good deal hindered by these demnition snows and frosts […]
adverb
(euphemistic, obsolete) Damned, very.
1918, Clarence Herbert New, The Unseen Hand: Stories of Diplomatic Adventure, New York: Caldwell, Chapter 1, p. 12,
They read a bloomin’ magazine story clear through from start to finish—written by a man who’s not even English, I’m told—an’ then are so demnition thick they don’t even know it’s pure fiction!