Esther is called Hadassah because she fills the world like myrtle fragrance.
Targum Sheni on (Esther 2:7) turns her names into prophecy. Hadassah means myrtle, and the righteous are compared to myrtle because their good works spread sweetness. The targum then reads Isaiah's promise that the fir and myrtle will rise in place of thorn and briar as a hidden map of the Purim story.
The thorn is Haman, who will rise in place of righteous Mordecai only to fall. The briar is Vashti, who will lose the throne so that Esther, the myrtle, can rise. The verse becomes a botanical prophecy of reversal.
That image changes Esther's introduction. She is not only an orphan raised by Mordecai, and not only the woman whose beauty brings her into the palace. She is the fragrant plant that appears where a harmful growth stood before. The Purim miracle begins quietly, as a myrtle growing in the shadow of thorns.