Green’s Dictionary of Slang

no! absolutely not! thus used as n. (see cite 1990).

1955		L.F. Engler ‘Gloss. Air Force Sl.’ AS XXX:2 118: Negative; Negatory; Negatrix; Negatron. I refuse; I disagree; no (in answer to a question).
1988		Eble Campus Sl. Mar. 7: negatory – no.
1990		W.D. Myers Mouse Rap 19: ‘Wouldn’t you prefer being called Freddie?’ Mr. D turns to me and asks. [...] ‘That is a big negatory,’ I answered. ‘A very big negatory.’ .
1997–2000		College Sl. Research Project (Cal. State Poly. Uni., Pomona) 🌐 Negatory (int.) No; I don’t think so; No way.
2014		B. Kroeber ‘Be My Alibi’ in ThugLit Sept. [ebook] Let’s meet up [...] Negatory.