E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
meant originally a private person, one not engaged in any public office. Hence Jeremy Taylor says, Humility is a duty in great ones, as well as in idiots (private persons). The Greeks have the expressions, a priest or an idiot (layman), a poet or an idiot (prose-writer). As idiots were not employed in public offices, the term became synonymous with incompetency to fulfil the duties thereof. (Greek, idiots.) (See BARON.)