Where does “functus” come from?

functus (Latin) comes from Latin fungor, from Proto-Indo-European bʰewg- — to flee; to enjoy, benefit.

Ancestry of “functus”, step by step

Step	Language	Word	Meaning
1	Latin	fungor	I perform, execute, administer, discharge,...
2	Proto-Indo-European	bʰewg-	to flee; to enjoy, benefit

functus — Etymology, Origin & Word History | Etymology Explorer