Where does “idle” come from?

idle (Old French) comes from Latin insula, from Latin in, from Old Latin en, from Proto-Italic en, from Proto-Indo-European h₁én — in.

Ancestry of “idle”, step by step

Step	Language	Word	Meaning
1	Latin	insula	island; insula, a residential or apartment block...
2	Latin	in	in, at, on, upon, from; within, while in; into,...
3	Old Latin	en	in
4	Proto-Italic	en	in
5	Proto-Indo-European	h₁én	in

idle — Etymology, Origin & Word History | Etymology Explorer