Where does “nisso” come from?

nisso (Portuguese) comes from Portuguese em, from Old Portuguese en, from Latin în, from Latin en, from Proto-Italic en, from Proto-Indo-European h₁én — in.

Ancestry of “nisso”, step by step

nisso traces back through two separate lines of ancestry.

via Portuguese em

Step	Language	Word	Meaning
1	Portuguese	em	in; inside; within; on; on top of; in; at
2	Old Portuguese	en	in
3	Latin	în	in, at, on, upon, from (space)
4	Latin	en	lookǃ beholdǃ; reallyǃ?; come onǃ
5	Proto-Italic	en	in
6	Proto-Indo-European	h₁én	in

via Portuguese isso

Step	Language	Word	Meaning
1	Portuguese	isso	that; this; correct, that's it; that's right
2	Old Portuguese	esso	—
3	Latin	ipsum	accusative masculine singular of ipse; nominative...
4	Latin	ipse	himself, herself, itself, the very, the actual;...
5	Proto-Italic	*e(s)peso	himself, herself, itself

Every word from Proto-Indo-European h₁én →Every word from Proto-Italic en →Every word from Latin en →