Where does “mesme” come from?

mesme (Norman) comes from Old French meïsme, from Vulgar Latin metipsimus, from Latin ipse, from Proto-Italic *e(s)peso.

mesme (Norman): same

Definitions

Step	Language	Word	Meaning
1	Old French	meïsme	Alternative form of mesme
2	Vulgar Latin	metipsimus	same
3	Latin	ipse	himself, herself, itself, the very, the actual;...
4	Proto-Italic	*e(s)peso	—

mesme — Etymology, Origin & Word History | Etymology Explorer