'archplagiarist' originates from Greek and Latin elements: the prefix 'arch-' (from Greek 'arkhē'/'arkhos') meaning 'chief' or 'principal', and 'plagiarist' (from Latin 'plagiarius', from 'plagium') where 'plagium' meant 'kidnapping' (later used for literary theft).

'archplagiarist' is a Modern English formation combining the English prefix 'arch-' with the established English noun 'plagiarist'. 'Plagiarist' itself came into English via Latin 'plagiarius' (and related forms in Medieval/Modern French) and developed the sense 'one who steals another's written work'.

The parts originally meant 'chief' and 'kidnapper', but over time 'plagiarist' shifted to mean 'one who copies or steals another's intellectual work', so 'archplagiarist' now means 'the chief or most egregious plagiarist'.