Where does “ultimō” come from?

ultimō (Latin) comes from Latin ultimus, from Proto-Italic *oltm̥mos.

Ancestry of “ultimō”, step by step

Step	Language	Word	Meaning
1	Latin	ultimus	last, final; furthest, farthest
2	Proto-Italic	*oltm̥mos	—

ultimō — Etymology, Origin & Word History | Etymology Explorer