Latin word protinus comes from Proto-Indo-European *pr̥-, Proto-Indo-European *tengʰ-

Detailed word origin of protinus

Dictionary entry	Language	Definition
*pr̥-	Proto-Indo-European (ine-pro)
*tengʰ-	Proto-Indo-European (ine-pro)
protinus	Latin (lat)	Continuously, constantly, uninterruptedly. Forward, farther on, onward. Immediately.