LATIN DICTIONARYLexicon Latīnum
proper noun · masculinesecond declension

Arīus1

Arīus m sg (genitive Arīī)
Classical[aˈriː.ʊs]Ecclesiastical[aˈriː.us]

Meaning

  1. a male given name from Ancient Greek, held most famously by Arius, Christian theologian and proverbial heretic (c. 250 – 336 CE)

Declension

declension
formsingularplural
nominativeArīus—
genitiveArīī—
dativeArīō—
accusativeArīum—
ablativeArīō—
vocativeArī—

Ărī^us (Arr-), i, m., = Ἀρεῖος or Ἄριος,
I. a renowned heretic, also ārĭus, Prud. Psych. 794.—Hence, ărīānus, a, um, adj., pertaining to Arius, Arian, Hier. adv. Lucif. 7.—ărīāni, ōrum, m., the followers of Arius, the Arians, Hier. adv. Lucif. 7; Aug. Haeres. 49.

Origins

Borrowed from Ancient Greek Ἄρειος (Áreios, from Ἄρης (Árēs, “Ares”) + -ιος (-ios)).

In the Academy Smith's classical dictionaries

proper noun · masculinesecond declension
Arius2
Arius m sg (genitive Ariī or Arī)
Classical[ˈa.ri.ʊs]Ecclesiastical[ˈaː.ri.us]

Meaning

  1. masculinesingularThe main river of Aria, now the Hari (Afghanistan)

Declension

declension
formsingularplural
nominativeArius—
genitiveAriī
Arī
—
dativeAriō—
accusativeArium—
ablativeAriō—
vocativeArī—

Ărī^us, i, m., = Ἄρειος or Ἄριος,
I. a river in Aria, now Heri, Plin. 6, 23, 25, § 93; in Amm. 23 fin. Arias.

Origins

Borrowed from Ancient Greek Ἀριός (Ariós).

In the Academy Smith's classical dictionaries

Quick answers

What does Arīus mean in Latin?
Arīus, a proper noun, means “a male given name from Ancient Greek, held most famously by Arius, Christian theologian and proverbial heretic (c. 250 – 336 CE)”.
What is the genitive of Arīus?
The genitive singular is Arīī. Arīus is masculine, second declension.
How do you pronounce Arīus?
In classical Latin, [aˈriː.ʊs]; in ecclesiastical (church) Latin, [aˈriː.us].