Arminius vs Armin

Arminius and Armin both are nouns.

Word	Noun	Adjective	Verb	Adverb
Arminius	Yes	No	No	No
Armin	Yes	No	No	No

As nouns, Arminius and Armin are synonyms defined as:

Arminius and Armin: German hero; leader at the battle of Teutoburger Wald in AD 9 (circa 18 BC - AD 19)

Other synonyms of Arminius include Hermann.

Arminius (noun)	Armin (noun)
German hero; leader at the battle of Teutoburger Wald in AD 9 (circa 18 BC - AD 19)	German hero; leader at the battle of Teutoburger Wald in AD 9 (circa 18 BC - AD 19)
Dutch Protestant theologian who founded Arminianism which opposed the absolute predestinarianism of John Calvin (1560-1609)