'archtraitor' originates as an English formation combining the prefix 'arch-' (from Greek 'arkhós' meaning 'chief' or 'principal') with the word 'traitor' (from Latin 'traditor', itself from 'tradere' meaning 'to hand over').

'archtraitor' appears as the hyphenated form 'arch-traitor' in earlier English usage and later is written as the solid compound 'archtraitor' in modern usage.

Initially it literally meant 'chief traitor' (the principal among traitors); over time it has been used more broadly as an emphatic epithet for an especially treacherous person.