Green’s Dictionary of Slang

wizard adj.

[despite US origin, the main use has been UK society, esp. by those who attended prep schools]

(orig. US) a general term of approval, excellent, wonderful; thus constr. with a, an excellent example.

[US]S. Lewis Babbitt 216: The Rev. Dr. John Jennison Drew [...] is a wizard soul-winner.
E. Waugh Black Mischief 277: They [...] righted themselves and stopped dead within a few feet of danger. ‘Wizard show that,’ remarked the pilot.
[NZ]N. Marsh Died in the Wool (1963) 60: He’d got a wizard of a camera.
[UK]G. Gibson Enemy Coast Ahead (1955) 50: God, look at those bags under his eyes; he must have had a wizard time!
[UK]A. Buckeridge Jennings’ Diary 241: Isn’t it wizard to think we’re going home in a few hours from now, sir?
[UK]J.P. Carstairs Concrete Kimono 110: A perfectly wizard idea.
[US]‘Iceberg Slim’ Airtight Willie and Me 165: The good old days of wizard torsos.
[UK]R. Dahl Rhyme Stew (1990) 34: I’ve got a wizard plan.
[UK]Guardian Editor 8 Oct. 20: It was absolutely wizard to hear gunfire.
[US]F.X. Toole Pound for Pound 13: Och, paddy, he’s wizard.

In derivatives