Green’s Dictionary of Slang

1. usu. of a machine or engine, broken, no longer working.

1916		‘I Want a G-Nôme’ in C.H. Ward-Jackson Airman’s Song Book (1945) 26: Give me the spluttering, conking G-nôme.
1919		J. Buchan Mr Standfast (1930) 606: Archie passed back a slip of paper on which he had scribbled: ‘Engine conked. Must land at Micklegill. Very sorry.’.
1925		(con. WWI) Fraser & Gibbons Soldier and Sailor Words 138: Konked (Konked Out): An Air Force term used of an aeroplane engine stopped working [...] a general expression meaning ‘knocked out’, dead.
1940		S. Longstreet Decade 310: Too bad the giants are gone. Conked out, dead and buried, or selling shoe-laces.
1978		H.C. Bosman Street-Women in Gray Theatre One 19: Your nerves is just conked in.
2017		A. Parks Bloody January 292: A bus had conked out in the snow in Argyle Street.

2. in ext. or fig. use, of a person, collapsed, asleep, dead.

1936		W.J. Blackledge Legion of Marching Madmen 109: ‘[H]how’n hell you going to find the dame? She may be conked out by now’.
1958		H. Ellison ‘With a Knife in her Hand’ in Deadly Streets (1983) 130: Is he conked?
1961		J. Kirkwood There Must Be a Pony! 70: The dogs were conked out in the trophy room.
1968		T. Wolfe Electric Kool-Aid Acid Test (1969) 84: One moment all conked out, but with her eyes open, staring.
1974		(con. 1945) E. Thompson Tattoo (1977) 357: He [...] hurried to where Pete lay like a conked supplicant before a cross.
1979		S. King Dead Zone (1980) 101: The patient was completely conked out.
1999		Scotland on Sunday mag. 7 Nov. 17: If I didn’t take heroin, I would be on the floor conked out with the skitters, shaking, being sick, hot and cold sweats.
2010		K. Richards Life 403: Everyone else is conked out on the floor.
2015		T. Pluck ‘Big Snip’ in Life During Wartime (2018) 25: A couple had a stroller with their conked out child.
2020		G. Krauze What They Was 101: Rah, ain’t my man gonna be concked out nah?
2023		(con. 1962) J. Ellroy Enchanters 409: Jack K. remained conked at the fuck pad.