'archconspirator' originates from a combination of Greek and Latin-derived elements: the prefix 'arch-' (from Greek 'arkhē') meaning 'chief, principal', and 'conspirator' (from Latin 'conspirator', from 'conspirare') where 'con-' meant 'together' and 'spirare' meant 'to breathe'.

'archconspirator' developed in Modern English by compounding the productive prefix 'arch-' with the existing noun 'conspirator' (itself from Latin 'conspirator' via Late Latin/Old French), producing the sense 'chief conspirator'.

Initially formed to denote the leading participant in a conspiracy, its meaning has largely remained stable as 'the principal plotter' in modern usage.