Where does “si si” come from?

si si (Limburgish) comes from Spanish sí, from Old Spanish sy, from Latin sīc, from Latin sice, from Latin sī, from Proto-Italic sei, from Proto-Indo-European só — this; that.

si si (Limburgish): of course!

Definitions

of course!

Ancestry of “si si”, step by step

Step	Language	Word	Meaning
1	Spanish	sí	yes, affirmation. Commonly used to respond...
2	Old Spanish	sy	yes in response to a question
3	Latin	sīc	yes, indeed (If answering a question)
4	Latin	sice	—
5	Latin	sī	if, supposing that
6	Proto-Italic	sei	so, thus
7	Proto-Indo-European	só	this; that

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