-arius

• (Classical) IPA^(key): /ˈaː.ri.us/, [ˈäːriʊs̠]
• (modern Italianate Ecclesiastical) IPA^(key): /ˈa.ri.us/, [ˈäːrius]

From earlier *-ās-(i)jo- (cf. Oscan sakrasias and Umbrian plenasier), formed from *-āso- (from PIE *-eh₂so-, cf. the Hittite appurtenance suffix -ašša-[1]), extended with the relational adjectival suffix *-yós (“belonging to”).

-ārius (feminine -āria, neuter -ārium); first/second-declension suffix

1. Used to form adjectives from nouns or numerals.

   ‎camera (“vault, arch”) + ‎-ārius → ‎camerārius (“climbing, creeping”)

   ‎ordō (“line, row”) + ‎-ārius → ‎ordinārius (“ordinary, of the rank and file”)

   ‎quaternī (“four at a time, by fours”) + ‎-ārius → ‎quaternārius (“quaternary”)

The nominative neuter form -arium, when appended to nouns, forms derivative nouns denoting a “place where things are kept”.

First/second-declension adjective.

(This etymology is missing or incomplete. Please add to it, or discuss it at the Etymology scriptorium.)

-ārius m (genitive -āriī or -ārī); second declension

1. (masculine only) -er; Used to form nouns denoting an agent of use, such as a dealer or artisan, from other nouns.

   ‎argentum (“silver”) + ‎-ārius → ‎argentārius (“banker”)

   ‎avicula (“little bird”) + ‎-ārius → ‎aviculārius (“bird keeper”)

   ‎rēte (“net”) + ‎-ārius → ‎rētiārius (“net fighter”)

Second-declension noun.

¹Found in older Latin (until the Augustan Age).