[zongk, zawngk]Slang.

verb (used without object) (often fol. by out)

to become unconscious from alcohol or narcotic drugs; pass out.
to fall soundly asleep or relax completely: I've got to go home and zonk out.

verb (used with object)

to stupefy, as by alcohol or narcotic drugs.
to sedate or anesthetize: If the pain gets too bad the doctors will zonk you.
to strike or defeat soundly; knock out; clobber.

Origin of zonk

1945–50; of expressive orig.; -onk perhaps copies conk2
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Word Origin and History for zonk

1950, "to hit hard;" 1968, "to put into a stupor;" slang term, of echoic origin.

Online Etymology Dictionary, © 2010 Douglas Harper