Where does “ординарный” come from?

ординарный (Russian) comes from Latin ōrdinārius, from Latin -ārius, from Proto-Italic *-āzios.

Ancestry of “ординарный”, step by step

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