Peloponnese UK /ˌpɛləpəˈniːz/US /ˌpɛləpəˈniːs/ noun2 •A peninsula in Greece, separated from mainland Europe by the Gulf of Corinth and connected to it by the Isthmus of Corinth. •A periphery of Greece containing Achaea, Arcadia, Argolis, Corinthia, Elis, Laconia, and Messenia.