Peloponnesian Peninsula vs Peloponnesus

Peloponnesian Peninsula and Peloponnesus both are nouns.

Word	Noun	Adjective	Verb	Adverb
Peloponnesian Peninsula	Yes	No	No	No
Peloponnesus	Yes	No	No	No

As nouns, Peloponnesian Peninsula and Peloponnesus are synonyms defined as:

Peloponnesian Peninsula and Peloponnesus: the southern peninsula of Greece; dominated by Sparta until the 4th century BC

Other synonyms of Peloponnesian Peninsula include Peloponnese.

Peloponnesian Peninsula (noun)	Peloponnesus (noun)
the southern peninsula of Greece; dominated by Sparta until the 4th century BC	the southern peninsula of Greece; dominated by Sparta until the 4th century BC