Where does “Фадей” come from?

Фадей (Russian) comes from Ancient Greek Θαδδαῖος, from Biblical Hebrew תַדַּי.

Ancestry of “Фадей”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Θαδδαῖος	—
2	Biblical Hebrew	תַדַּי	—

Фадей — Etymology, Origin & Word History | Etymology Explorer