Where does “Zelus” come from?

Zelus (English) comes from Ancient Greek Ζῆλος, from Proto-Indo-European yeh₂- — to go; to go in, enter; to ride, to travel.

Ancestry of “Zelus”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	Ζῆλος	—
2	Proto-Indo-European	yeh₂-	to go; to go in, enter; to ride, to travel