Where does “Arcady” come from?

Arcady derives from English poetic usage of Ancient Greek Ἀρκαδία, the name of a region in the Peloponnese associated with pastoral imagery.

Ancestry of “Arcady”, step by step

Step	Language	Word	Meaning
1	Russian	Арка́дий	—
2	Ancient Greek	Ἀρκάδιος	—
3	Ancient Greek	-ῐος	belonging to; of”, “belonging to”, “pertaining to
4	Proto-Indo-European	-yós	Creates adjectives from noun or verb stems