Where does “seu” come from?

seu (Old Portuguese) comes from Latin suus, from Proto-Italic sowos, from Proto-Indo-European sewos, from Proto-Indo-European swé — self.

seu (Old Portuguese): third-person singular possessive pronoun: his,...

Definitions

Step	Language	Word	Meaning
1	Latin	suus	his, her, its, their
2	Proto-Italic	sowos	his, her, its, their
3	Proto-Indo-European	sewos	(one's) own; his, her, its
4	Proto-Indo-European	swé	self