Where does “sustenire” come from?

sustenire (Vulgar Latin) comes from Latin sustineo, from Latin sub-, from Proto-Indo-European upó, from Proto-Indo-European h₃ewp-.

Ancestry of “sustenire”, step by step

Step	Language	Word	Meaning
1	Latin	sustineo	I hold up or upright, uphold, keep up, bear up,...
2	Latin	sub-	sub-
3	Proto-Indo-European	upó	under, below
4	Proto-Indo-European	h₃ewp-	—

sustenire — Etymology, Origin & Word History | Etymology Explorer