The most shameful or notorious turncoat; one who betrays allegiance in the most egregious way.
From 'arch-' (chief) plus 'turncoat' (a person who switches sides, from the image of wearing a reversible coat with different colors). This compound intensifies the moral condemnation of switching loyalties.
During wars and revolutions, calling someone an 'archturncoat' was basically medieval Twitter insults—it was the harshest accusation you could level against a noble or soldier. The term shows how language weaponizes betrayal!
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