Past tense of blackjack; struck with a blackjack (a weapon), or in card games, achieved 21 with two cards.
From 'blackjack' (a weapon made from a leather tube filled with lead or sand, or the card game) plus past tense '-ed.' The weapon derives from the card game term, which comes from 'Black Jack' the variant of '21.'
The blackjack weapon was outlawed in many places because it could deliver devastating blows without leaving obvious wounds—it was the 'stealth weapon' of the 19th-20th centuries, which is why it became so closely associated with crime and thuggery.
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