Where does “exterus” come from?

exterus (Latin) comes from Latin exter, from Proto-Italic *eksteros.

exterus (Latin): Alternative form of exter; on the outside,...

Definitions

Step	Language	Word	Meaning
1	Latin	exter	On the outside, outward, external, outer; Of...
2	Proto-Italic	*eksteros	—

exterus — Etymology, Origin & Word History | Etymology Explorer