Tarquinius vs Tarquin

Tarquinius and Tarquin both are nouns.

Word	Noun	Adjective	Verb	Adverb
Tarquinius	Yes	No	No	No
Tarquin	Yes	No	No	No

As nouns, Tarquinius and Tarquin are synonyms defined as:

Tarquinius and Tarquin: according to legend, the seventh and last Etruscan king of Rome who was expelled for his cruelty (reigned from 534 to 510 BC)

Other synonyms of Tarquinius include Lucius Tarquinius Superbus, Tarquin the Proud, Tarquinius Superbus.

Tarquinius (noun)	Tarquin (noun)
according to legend, the seventh and last Etruscan king of Rome who was expelled for his cruelty (reigned from 534 to 510 BC)	according to legend, the seventh and last Etruscan king of Rome who was expelled for his cruelty (reigned from 534 to 510 BC)