Green’s Dictionary of Slang

(orig. US black) ideal, perfect, excellent, quintessential.

1941		Cab Calloway ‘Are You All Reet?’ 🎵 Are you all reet? / Jump in the groove and go!
1943		New Yorker 19 June 15: ‘All reat’ [...] is the rug-cutter’s way of saying ‘all right’.
1944		D. Burley Orig. Hbk of Harlem Jive 12: That fine banana [...] understand, is as mellow as a cello; as fine as red wine; a killer from Manila; like the tree, ole man, understand?, all root.
1950		S.J. Baker in Sun. Herald (Sydney) 8 June 9/4: Among American borrowings recorded in Detective Doyle's list are: [...] ‘hophead,’ a drug addict; ‘reet,’ right or O.K. [etc].
1953		L. Durst Jives of Dr. Hepcat (1989) 7: Jackson when I finish with the mop everything will be much reet.
1960		Mad mag. June 48: Swinging, hip and real gone reet trick.
1974		(con. 1940s) E. Thompson Tattoo (1977) 241: ‘Well, all reet!’ He turned rubbing his hands together eagerly.
1983		S. King Christine 246: They were feeling pretty much reet and compleet.
2000		Guardian Rev. 27 May 12: That’s reet champion, that is!