Where does “ostiārius” come from?

ostiārius (Latin) comes from Latin -ārius, from Proto-Italic *-āzios.

Ancestry of “ostiārius”, step by step

Step	Language	Word	Meaning
1	Latin	-ārius	—
2	Proto-Italic	*-āzios	—

ostiārius — Etymology, Origin & Word History | Etymology Explorer