Where does “si” come from?

si (Guinea-Bissau Creole) comes from Portuguese sé, from Old Portuguese se, from Latin sī, from Proto-Italic sei, from Proto-Indo-European só — this; that.

si (Guinea-Bissau Creole): if

Definitions

Ancestry of “si”, step by step

Step	Language	Word	Meaning
1	Portuguese	sé	see
2	Old Portuguese	se	if
3	Latin	sī	if, supposing that
4	Proto-Italic	sei	so, thus
5	Proto-Indo-European	só	this; that

Every word from Proto-Indo-European só →Every word from Proto-Italic sei →Every word from Latin sī →