Green’s Dictionary of Slang

(US) an emphatic ‘no!’.

1855		Broadway Belle (N.Y.) 29 Oct. 1/3–4: Nixey tipping the slums but sherry down the kid with my other benjamin and a slum or two, for the peck is awful quisby.
1879		Cincinnati Enquirer 7 Sept. 10/7: Nixey means ‘no’ or ‘don’t,’ and [...] is considered as strong as the most emphatic ‘no.’.
1887		World (N.Y.) 26 Aug. 6/4: The Louisville German thought he had jays to deal with. Nixey, Freddie; you were too rash.
1887		Cincinnati Enquirer (OH) 24 Dec. 12/2: Giving the young man a warning look, said: ‘Nixey, Toohey, don’t flash, blow it, man’ [...] which meant [...] Toohey ought not to talk quite so much.
1890		Harrisburg Teleg. (PA) 6 Nov. 3/4: ‘Nixy birdy!’ ‘Nixy’.
1900		Bulletin (Sydney) 22 Dec. 7/3: Well, when our officers called on all the men willing to join the new police to step out from the ranks, the result was ‘nixy,’ for not a pilgrim budged an inch.
1901		W. Irwin Love Sonnets of a Hoodlum XV n.p.: Nixie! I’m not canned chicken till I’m cooked.
1902		Ade Girl Proposition 120: I have learned to put a Nixey Label on the Man who tells all he Knows.
1904		C. Connors Bowery Life [ebook] Nixey, dey ain't no good. A guy wot's hungry can't eat de cover off a book, kin he.
1912		A. Berkman Prison Memoirs of an Anarchist (1926) 163: Refuse? Me? Nixie.
1914		Ade ‘The New Fable of the Aerial Performer’ in Ade’s Fables 210: He wanted to stick around and parlee up to a Billion, but she raised a most emphatic Nixey.