What does "conk out" mean?

To fall fast asleep; to sleep soundly.

What is a synonym for "conk out"?

Common synonyms include: be done for, be no more, break, break, break down, break down.

verb, slang

verb, slang ·Common ·High school level

Verb

1
To fall fast asleep; to sleep soundly. informal, intransitive
"He wasn't there, just the dog, conked out on the porch."
2
use up all one's strength and energy and stop working wordnet
3
To stop functioning. informal, intransitive
"The old car conked out halfway up the hill."
4
stop operating or functioning wordnet
5
To die. informal, intransitive
"He lived to be 90, then conked out in his sleep."

"He wasn't there, just the dog, conked out on the porch."

Possibly an onomatopoeic imitation of the sound of a stalling internal combustion engine. Possibly coined by British motorcyclists circa 1910.