To me, Zaynab looks like the Arabisation of Zenobia (A historical Zenobia was queen of Palmyra). The internal Arabic explanations aren't convincing to me because the type of word compounding needed isn't productive in Arabic language. [noted -ed]
Zaynab is Arabic word and came from Arabic words "zayn" and "ab". ZAYN means beauty and AB means father. So zaynab means beauty of father as per Arabic dictionary. And most famous personality is the daughter of ALI (a.s.) son of ABU TALIB (a.s.)