Where does “residu” come from?

residu (Old French) comes from Latin residuum, from Latin residuus, from Latin resideō, from Latin sedeō, from Proto-Italic sedēō, from Proto-Indo-European sḗd- — to sit.

Ancestry of “residu”, step by step

Step	Language	Word	Meaning
1	Latin	residuum	nominative neuter singular of residuus;...
2	Latin	residuus	remaining; residuary; persisting, surviving
3	Latin	resideō	to reside, abide, tarry, linger
4	Latin	sedeō	to sit, to be seated
5	Proto-Italic	sedēō	sit, be sitting, be seated
6	Proto-Indo-European	sḗd-	to sit

Words derived from “residu”

Every word from Proto-Indo-European sḗd- →Every word from Proto-Italic sedēō →Every word from Latin sedeō →