Green’s Dictionary of Slang

demnition adj.

a var. on damned adj.; also as adv (see cite 1890).

1848		‘Ned Buntline’ Mysteries and Miseries of N.Y. II 11: Harry, you’re a sad dog – a demnition sad dog!
1885		Bulletin (Sydney) 31 Oct. 12/4: A Melbourne organ-grinder has been robbed of £250 – ‘his savings of the past year.’ We can’t save £5 a week out of our ‘demnition grind.’.
1890		Bird o’ Freedom 1 Jan. 1/4: Demnition sweetness!
1890		Music Hall & Theatre Rev. 29 Nov. 7/2: Performing dogs I do not care much about as a rule. At times they look so ‘demnition miserable’.
1894		Truth (Sydney) Feb. 1/7: ‘Demonfort’ is a demnition good name for a gaoler.
1902		Ade Forty Modern Fables 165: He wanted the Children to take the same Gloomy View of the whole Demnition Grind.
1904		Sydney Sportsman (Surry Hills, NSW) 29 June 3/6: He cut himself entirely away from ‘the Golden West,’ and even America as a whole, and became a demnition Englishman, doncherkno.
1911		G. Stratton-Porter Harvester 538: Chilly! Demnition cold is what they are!
1940		E. Curry Hysterical Hist. of Aus. 31: The thoil lookth tho demnition muddy. [Ibid.] 188: : Dashed [...] if they’re going to allow any demnition thingumbobs into Melbourne.

In compounds