Where does “ultisol” come from?

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

Ancestry of “ultisol”, step by step

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

ultisol — Etymology, Origin & Word History | Etymology Explorer