Peloponnesus vs Peloponnesian Peninsula

Peloponnesus and Peloponnesian Peninsula both are nouns.

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

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

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

Other synonyms of Peloponnesus include Peloponnese.

Peloponnesus (noun)	Peloponnesian Peninsula (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