From BiblePortal Wikipedia

Smith's Bible Dictionary [1]

Hadas'sah. (Myrtle). Probably, the earlier name of Esther.  Esther 2:7.

Hastings' Dictionary of the Bible [2]

Hadassah (‘myrtle’). The Jewish name of Esther (  Esther 2:7 only). See Esther.

Fausset's Bible Dictionary [3]

Esther's original name ( Esther 2:7). Possibly the same name as "Atossa," Cyrus' daughter.

Holman Bible Dictionary [4]

 Esther 2:7Esther

Morrish Bible Dictionary [5]

Another name for Esther.  Esther 2:7 .

Easton's Bible Dictionary [6]

 Esther 2:7

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [7]

(Heb. Hadassah', הֲדִסָּה , Myrtle; comp. the Gr. names A Myrto, etc.; Sept. omits, Vulg. Edissa), the earlier Jewish name of ESTHER ( Esther 2:7). Gesenius (Thesaur. p. 366) suggests that it is identical with Σατοσσα , the name of the daughter of Cyrus (Herod. 3. 133,134).

International Standard Bible Encyclopedia [8]

ha - das´a ( הדסּה , hădhaṣṣāh , "myrtle"): The Hebrew name (  Esther 2:7 ) formerly borne by Esther (which see).