Where does “*(i)stipsum” come from?

*(i)stipsum (Vulgar Latin) comes from Latin istum, from Latin ipsum, from Latin ipse, from Proto-Italic *e(s)peso.

Ancestry of “*(i)stipsum”, step by step

Step	Language	Word	Meaning
1	Latin	istum	accusative masculine singular of iste
2	Latin	ipsum	accusative masculine singular of ipse; nominative...
3	Latin	ipse	himself, herself, itself, the very, the actual;...
4	Proto-Italic	*e(s)peso	—

*(i)stipsum — Etymology, Origin & Word History | Etymology Explorer