'archflatterer' is formed from the prefix 'arch-' (from Greek 'arkhos' meaning 'chief, principal') combined with 'flatterer' (one who flatters).

'arch-' entered English via Latin and Old French as a productive intensifying/prefix element; 'flatterer' evolved from Middle English 'flaterer' (from Old French 'flater' or similar imitative sources) to the modern English 'flatterer', and the compound 'archflatterer' arose in Modern English by joining these elements.

Initially, 'arch-' meant 'chief' and 'flatterer' meant 'one who flatters'; together the compound originally meant 'the chief flatterer' and has retained that core sense, though it is often used now with ironic or pejorative emphasis to indicate an extreme sycophant.