Green’s Dictionary of Slang

a general excl. of affirmation, approval: excellent, wonderful.

1972		(con. 1950s) Jacobs & Casey Grease II v: Hey, Sandy! Wow, what a total! Wick-ed!
1992		M. Frayn Now You Know 86: Look at that filthy grin! Wicked! He can’t get enough of it!
1999		Guardian G2 23 Aug. 4: Cheers Mam. Wicked! Thank you Mam.
2000		N. Barlay Crumple Zone 31: There’s applause from Stupid Slut, her permanently grinning boyfriend and galfriend and a round of wicked.
2011		S. Kelman Pigeon English 84: Connor green: ‘Wicked!’.