Green’s Dictionary of Slang

cold-deck v.2

[SE (out cold), unconscious/knock cold under knock v. + deck v.2 (1)]

to knock unconscious; occas. to kill.

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[US]D. Pendleton Boston Blitz (1974) 38: Maybe they already decided to write us off [...] Maybe they figure Boston is the least costly place to cold deck the guy.
[US]R. Price Blood Brothers 98: If a big kid were tormenting Albert, you wouldn’t hesitate to cold-deck him, right?