A-OK, phr. — Green’s Dictionary of Slang

A-OK phr.

also A-okay

[A-1 adj. (1) + OK adj. (1); originated in spaceflight jargon and spread to the wider public after the broadcast of the Mercury flight of Commander Alan Shepard (1923–98) on 5 May 1961]

intensifier of OK, all’s well, everything’s absolutely fine.

1959		in Webster (9th edn).
1961		A. Shepard in Snyder & Morris Treasury of Great Reporting (1962) 767: Everything A- OK . . . Mission very smooth . . . What a beautiful view! ... His ‘A- OK’ is a rocket-engineer term meaning double OK or perfect.
1961		Omaha World-Herald 8 May 12: ‘A-okay,’ as everybody now knows, means all’s well, everything functioning perfectly.
1970		T. Southern Blue Movie (1974) 94: ‘Did Lazlo check it?’ Sid made a circle with his thumb and forefinger, and winked. ‘A-Okay, B.’.
1984		D. Jenkins Life Its Ownself (1985) 317: ‘How was it?’ ‘A-okay.’.