Green’s Dictionary of Slang

nit! excl.1

also nitz
[var. on SE not]

(US) used as an emphatic no, also added to positive assertions to give a negative meaning e.g., ‘I should say nit!’.

[US]Sun (NY) 21 May 28/1: ‘D’ye tink a Sister’ll let you die widout doin’ all she can fer ye? Nit, nit; I guess nit’.
[US]Ade Artie (1963) 9: I should say nit.
[UK]Mirror of Life 14 Mar. 3/3: How did jhe receive [the challenge]? With that stern joy that a true warrior feels in a foeman worthy of his steel? Nit.
[US]W.J. Kountz Billy Baxter’s Letters 5: I let go with the first barrel, right into the center of the bunch. Nit duck. Then the second barrel went off of its own accord. I’ll swear, Jim, I had nothing whatever to do with it. Anyway, nit duck.
[US]A.H. Lewis ‘Mulberry Mary’ in Sandburrs 10: But Mary says ‘Nit! couple of times nit!’.
[Aus]Sydney Sportsman (Surry Hills, NSW) 11 May 2/3: Nit, you ‘chain smokers’.
[US]‘O. Henry’ ‘A Lickpenny Lover’ in Voice of the City (1915) 30: Nit; he’s too cheap a guy for that.
[Aus]E. Dyson Spats’ Fact’ry (1922) 92: ‘What price bein’ bes’ man, Cobber?’ [...] ‘Nit. Not any in Georgie’s, please.’.
[US]AS II:11 475: List of the variants of ‘no’ [...] nope, nit, nitsky, nix, nixy, nah, naw, aber nit [etc.].
[US](con. 1890s) A.F. Harlow Old Bowery Days 493: Do you want to put me on the bum, like Tim Campbell and Sulzer? Nit!
[US]Life 5 Jan. 57: A fine bunch of statesmen they got in this town — nit.

In phrases

sing nitz (v.)

(Aus.) to say no, to reject.

[Aus]Truth (Brisbane) 25 July 3/4: ‘She promised me [...] that she was going to be a square-an’-all good kid, and sing nitz to the sweet stuff of any of yous mob’ .