A shepherd, a fancy farmer; so called because the Arcardians were a pastoral people, and hence pastoral poetry is called Arcadic.
An Arcadian youth. A dunce or blockhead; so called because the Arcardians were the least intellectual of all the Greeks. Juneval (vii. 160) uses the phrase Arcadicus juvenis for a stupid fool.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894