From BiblePortal Wikipedia

Hastings' Dictionary of the Bible [1]

Harbona (  Esther 1:10 ) or Harbonah (  Esther 7:9 ). The third of the seven eunuchs or chamberlains of king Ahasuerus. It was on his suggestion that Haman was hanged upon the gallows which he had prepared for Mordecai.

Smith's Bible Dictionary [2]

Har'bona. (Ass-Driver). The third of the seven chamberlains or eunuchs, who served King Ahasuerus.  Esther 1:10. (B.C. 483-475).

Fausset's Bible Dictionary [3]

Third of the seven eunuchs of Ahasuerus. Suggested the hanging of Haman on his own gallows ( Esther 1:19;  Esther 7:9).

Holman Bible Dictionary [4]

 Esther 1:10 Esther 7:9

Easton's Bible Dictionary [5]

 Esther 1:10 7:9

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [6]

(Heb. Charbona', חִרְבוֹנָא , prob. Pers. for Ass-Driver; Sept. Ο᾿Αρεβωά v.r. Θαρρά ), one of the seven eunuchs of king Ahasuerus or Xerxes, commanded by him to exhibit the beauty of Vashti ( Esther 1:10). He was probably the same with the one called HARBONAH (Heb. Charbonah, חִרְבוֹנָה , Id.; Sept. changes to Βουγαθάν ), who suggested to the king the idea of hanging Haman on his own gallows (chap. 7:9). B.C. 483473.