Green’s Dictionary of Slang

1. to hit or strike.

1954		A. Buckeridge According to Jennings (1991) 68: I’ll show you how he zonks a boundary over the bowler’s head.
1961		H. Ellison Rockabilly (1963) 61: He’ll probably want a few of those little Bufferin B’s zonking around in his system.
1977		E. Torres Q&A 87: He iced Julio Sierra; then he zonks Tony Roman and puts the gun on him.
2003		McGill Reed Dict. of N.Z. Sl.

2. to fail.

1968

Listener 14 Mar. 352/3: If Johnny zonked, it would be bad for my book.

3. (also zonk out) to fall asleep.

1968		Current Sl. II:3 16: Zonk out, v. To sleep.
1980		Eble Campus Sl. Spring 6: zonk out – to sleep heavily.
1989		Eble Campus Sl. Mar.
2001		K. Waterhouse Soho 77: If she turned out to have zonked off, would it count as rape?
2012		D. O’Donnell Locked Ward (2013) 251: Terry’s zonked again.
2023		Twitter 16 July 🌐 My vuwy sweepy baby on the train. I couldn’t be happier! To know he feels vulnerable and safe enough with me to just zonk out in public .

4. (US, also zonk out) to die, to lose consciousness, esp. from alcohol or drugs.

1980		(con. 1940s–60s) H. Huncke ‘Florence’ in Eve. Sun Turned Crimson (1998) 200: She had taken several Doraphen, and when the stuff hit her, she sort of zonked out.
1999		E. Bunker Mr Blue 238: I was disappointed that Sandy had zonked herself to heroin oblivion.

5. to overcome, to knock out, lit. or fig.

1972		R. Barrett Lovomaniacs (1973) 348: And — like that — it zonked me. A real gas!
1977		C. McFadden Serial 37: They [...] had been really zonked when Tony Wilson said the only thing that really worked was panther urine.