'archdolt' is a compound formed from the prefix 'arch-' (originating from Greek, specifically 'archi-' where 'archi-' meant 'chief' or 'principal') and the word 'dolt' (from earlier English, meaning 'stupid person').

'dolt' entered English usage in the 17th century as a term for a dull or stupid person; later, speakers formed emphatic compounds using the 'arch-' element, and the humorous/pejorative compound 'archdolt' was recorded subsequently as a way to mean 'extreme dolt'.

Initially it carried the sense of 'chief fool' or 'principal dolt' as an emphatic compound; over time it has retained that emphatic meaning as 'an extremely foolish person' (now archaic or humorous).