Where does “oisos” come from?

oisos (Old French) comes from Latin ōtiōsus, from Latin -ōsus, from Old Latin -ōssus.

Ancestry of “oisos”, step by step

Step	Language	Word	Meaning
1	Latin	ōtiōsus	—
2	Latin	-ōsus	—
3	Old Latin	-ōssus	—

oisos — Etymology, Origin & Word History | Etymology Explorer