Green’s Dictionary of Slang

(W.I.) just as well.

1915, 1977

cited in Cassidy & LePage Dict. Jam. Eng. (1980).

(US) very naïve, unsophisticated.

1984		N.Y. Times 5 Apr. n.p.: Mr. Lewis spent 22 years in police precincts in Brooklyn and Manhattan. He had not, as they say, just fallen off the turnip truck [R].
2006		L. Horton Fear Not 66: Mr. Gomes looked at me like I’d just fallen off the cabbage truck.

(Aus./N.Z.) just between you and me, confidentially.

1925		Wyalong Advocate (NSW) 27 Feb. 2/5: If they had done so, just how many of the feminine sex of this town would be promising themselves that they would be there — aye, and just quietly how many of the opposite sex would be enquiring just where this show was to be held — the whole bang lot, believe me.
1927		Truth (Sydney) 6 Mar. 11/3: The children's wonder-show — and just quietly, the grown-up’s [sic] — is coming back to Sydney next Thursday night.
1933		Week (Brisbane) 27 Sept. 4/1: [column title] Just Quietly. Dear Shipmates, If you hear that the new captain had to walk the plank [etc].
1941		Baker Popular Dict. Aus. Sl. 40: Just quietly, between you and I.
1951		(con. 1941) E. Lambert Twenty Thousand Thieves 123: That Chips Prentice is a soldier and a half. Just quietly, he’s up for a decoration.

(Aus.) exactly what one requires.

1941

Baker Popular Dict. Aus. Sl.