Where does “stiass” come from?

stiass (Dalmatian) comes from Vulgar Latin st + ipsu, from Latin ipsum, from Latin ipse, from Proto-Italic *e(s)peso.

stiass (Dalmatian): same

Definitions

Step	Language	Word	Meaning
1	Vulgar Latin	st + ipsu	—
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	—

stiass — Etymology, Origin & Word History | Etymology Explorer