Where does “رب” come from?

رب (Classical Persian) comes from Arabic رَبّ, from Proto-Semitic rabb- — to expand, to extend; lord, owner, chief;...

Ancestry of “رب”, step by step

Step	Language	Word	Meaning
1	Arabic	رَبّ	lord, master; God; Lord; Lord
2	Proto-Semitic	rabb-	to expand, to extend; lord, owner, chief;...