Green’s Dictionary of Slang

(US) without a doubt, irrefutably.

1914		Syracuse Herald 27 Mar. 8/3: ‘Postolutely you’re right!’ Gus declared, also giving Mr. Blodger a scornful glance. ‘As long as he loses his money I’ll shake dice with him, but socially I wouldn’t have anything to do with him. Absotively and postolutely not!’.
1922		L.J. Vance Linda Lee, Incorporated 190: ‘If we stick in anybody that hasn’t,’ Jacques interpolated, ‘the whole works will postolutely go ker-flooey.’.
1926		Wood & Goddard Dict. Amer. Sl.
1947		Ryerson & Clements Divine Flora 38: Posilutely! [MRS. PRYOR bustles down, followed by her husband, who has left his sweater-coat upstairs].
1953		S. Harris Father Divine, Holy Husband 52: For slightly larger fees, they sold numbers ‘absotively posilutely’ guaranteed to win on the next day’s policy wheel.
1968		B. Dryer Torch Bearers 148: The most posolutely absotively gorgeous hunk .
1986		L. Braun A Stone Watermelon 140: ‘Posilutely,’ answered Jason, [...] ‘Haven’t I told you not to play with your food?’.
1993		L. Sanders McNally’s Risk 100: You’re posilutely insatiable.
2004		B.W. Anderson Hide Park 145: He glanced down and he absotively, posilutely FREAKED!