Esther 2:7

7. Hadassah, that is, Esther Tyrwhitt regards Hadassah as the court name, by which she was known among the Persians, and Esther as her Jewish maiden name, by which she was known to her own people. But to this it may be fairly replied that she would be more likely to be known to her own people as well as to the Persians by her royal name; and most interpreters have naturally understood from the expression, he brought up Hadassah, which is Esther, that Hadassah was her early maiden name, and that she took the name of Esther when she became queen. Moreover Hadassah is of Semitic origin, and signifies myrtle; while Esther is the Persian word for star, (Greek, αστηρ .) The fair and beautiful maiden was known as myrtle; the brilliant and fascinating queen was called star. The name Hadassah is, indeed, substantially identical with Atossa, mentioned by the Greek writers as the wife of Darius Hystaspes, and daughter of Cyrus, but the identity in name is insufficient to identify the Jewish virgin with one who is so clearly represented by Herodotus as both daughter of Cyrus and widow of Cambyses. ( Herodotus, 3:88.)

His uncle’s daughter This uncle’s name was Abihail. Esther 2:15. Mordecai and Esther were cousins, but Mordecai was evidently much the older.