'arcadia' originates from Greek, specifically the word 'Ἀρκαδία' (Arkadía), originally the name of a district in the Peloponnese associated with the mythic figure Arcas.

'Ἀρκαδία' entered Latin as 'Arcadia' and was adopted into Middle English largely unchanged, eventually becoming the modern English 'arcadia' (plural 'arcadias').

Initially it meant 'the region of Arcadia' (a specific geographical area), but over time it evolved into its current broader meaning of 'an idealized pastoral paradise' (and thus into literary and figurative uses).