Green’s Dictionary of Slang

(usu. juv., except when ironic) wonderful, brilliant, amazing; also as excl.

[1905		Eng. Dial. Dict. ].
1943		in Penguin New Writing No. 16 28: Wizzoh! No night fighters!
1944		A. Morrison letter 5 Jan. in Morrison Things My Mother Never Told Me (2002) 90: I’ve got a wizzo billet – fire and wash basin in room.
1950		A. Buckeridge Jennings Goes To School 37: Super-duper! And wizzo!
1958		Willans & Searle Complete Molesworth (1985) 14: So BOYS triumphant agane WIZZ.
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 181: Other superlatives in favour were: [...] whiz-bang, whizzo, whizzol, and wizard.
1968		Listener 19 Dec. 810/3: The Squadron-Leader and I decided to give a party — what the Squadron-Leader called a proper whizzo party with marks on the ceiling .
1983		M. Read Scouting for Boys in Best Radio Plays (1984) 141: Red hot news! Absolutely whizzo!
1986		R.G. Barrett Godson 22: ‘This is all supposed to a bit of a whizzo bash’.