Where does “Θαδδαῖος” come from?

Θαδδαῖος (Ancient Greek) comes from Biblical Hebrew תַדַּי.

Ancestry of “Θαδδαῖος”, step by step

Step	Language	Word	Meaning
1	Biblical Hebrew	תַדַּי	—

Θαδδαῖος — Etymology, Origin & Word History | Etymology Explorer