From BiblePortal Wikipedia

Fausset's Bible Dictionary [1]

Queen of Ahasuerus or Xerxes (Esther 1 and Esther 2). Refused to appear at the king's command, to exhibit her beauty before the king's guests at a banquet; was therefore deposed and repudiated lest a precedent should be given for insubordination of wives to husbands. Vashti may answer to Amestris the queen consort throughout Xerxes' reign, and queen mother under his son and successor - Artaxerxes.

But more probably she and Esther were only "secondary wives" with the title "queen." Plutarch (Conjug. Precept. c. 16, in agreement with Herodotus v. 18) says the Persian kings had their legitimate wives to sit at table, but when they chose to drink and revel they sent away their wives and called in the concubines, it was when his "heart was merry with wine" that he sent for Vashti as a concubine; but she, looking on herself as a legitimate wife, would not come.  Esther 5:4;  Esther 5:8;  Esther 5:12, shows that it was no impropriety for wives to be at banquets in front of other men (besides their husbands).

Smith's Bible Dictionary [2]

Vash'ti. (Beautiful). The "queen" of Ahasuerus, who, for refusing to show herself to the king's guests at the royal banquet, when sent for by the king, was repudiated and deposed.  Esther 1:1. (B.C. 483). Many attempts have been made to identify her with historical personages; but it is far more probable that she was only one of the inferior wives, dignified with the title of queen, whose name has utterly disappeared from history.

Holman Bible Dictionary [3]

 Esther 1:9 Esther 1:19 Esther 2:16AhasuerusEstherPersiaXerxes

Morrish Bible Dictionary [4]

Queen of Ahasuerus, whom he repudiated on account of her refusing to show her beauty before the people and princes at the king's feast.  Esther 1:9-19;  Esther 2:1,4,17 .

American Tract Society Bible Dictionary [5]

The queen of Persia, divorced by Ahasuerus or Xerxes her husband for refusing to appear unveiled before his reveling company,  Exodus 1:1 -  22 .

People's Dictionary of the Bible [6]

Vashti ( Văsh'Ti ), Beautiful. The deposed "queen" of Ahasuerus.  Esther 1:1-22. b.c. 483.

Hastings' Dictionary of the Bible [7]

VASHTI (  Esther 1:9;   Esther 1:11 etc.). See Esther [Book of], 3.

Easton's Bible Dictionary [8]

 Esther 1:10-12Esther

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [9]

(Heb. Vashti', וִשְׁתַּי , Pers. Beautiful woman; Sept. Ἀστίν ; Josephus Ούσάτη ; Vulg. Vasthi ) , the "queen" ( הִמִּלְכָּה ) of Ahasuerus (Xerxes), who, for refusing to show herself to the king's guests at the royal banquet, when sent for by the king, incurred his wrath, and was repudiated and deposed (Esther 1), when Esther was substituted in her place. B.C. 483. Many attempts shave been made to identify her with historical personages; as by Usher With Atossa, the wife of Darius Hystaspis, and by J. Capellus with Parysatis, the mother of Ochus; but, as was said of Esther (like the "threescore queens" in  Song of Solomon 6:8-9; comp. Herod. 1, 135), it is far more probable that she was only one of the inferior wives, dignified with the title of queen, whose name has utterly disappeared from history. (See Esther). This view of Vashti's position seems further to tally exactly with the narrative of Ahasuerus's order, and Vashti's refusal, considered with reference to the national manners of the Persians. For. Plutarch ( Conjug. Praecept. c. 16) tells us, in agreement with Herod. 5, 18, that the kings of Persia have their legitimate wives to sit at table with them at their banquets; but that, when they choose to riot and drink, they send their wives away and call in the concubines and singing-girls. Hence, when the heart of Ahasuerus "was merry with wine," he sent for Vashti, looking upon her only as a concubine; she, on the other hand, considering herself as one of the Κουριδίαι Γυναῖκες , or legitimate wives, refused to come. Josephus's statement ( Ant. 11 :6, 1) that it is contrary to the customs of the Persians for their wives to be seen by any men but their own husbands is evidently inaccurate, being equally contradicted by Herodotus (5, 18) and by the book of Esther itself (5, 4, 8, 12, etc.).

International Standard Bible Encyclopedia [10]

vash´tı̄ ( ושׁתּי , washtı̄  ; Ἀστίν , Astı́n  ; Old Persian "beautiful woman"): The former queen of Xerxes, whom he divorced. On the 7th day of a great feast which the king was giving to the assembled nobles of the empire and others, he commanded the seven chamberlains who served in his presence to bring the queen into the assembly. We are told (  Esther 1:11 ) that his purpose was "to show the peoples and the princes her beauty; for she was fair to look on." The king's command was met by Vashti with a mortifying refusal to obey. The reason which is sometimes assigned for her disobedience - that no man but the king was permitted to look upon the queen - is without foundation. Esther invites Haman on two occasions to accompany the king to a banquet at which she was present. Nor can it be said that there was any lack of recognition of Vashti's high dignity; the seven highest officials of the palace were sent to escort her. The refusal had to be visited with a punishment severe enough to reestablish the supremacy which it threatened to overthrow. She was, accordingly, divorced and dethroned.

There is no known reference to Vashti outside of Esther. The suggestion has been made that Vashti was an inferior wife, or one of the royal concubines. There is nothing, however, to support it; and it is, besides, directly opposed to several statements in the narrative. She is always named "queen" ( Esther 1:9 ,  Esther 1:11 ,  Esther 1:12 ,  Esther 1:15-18 ). It is only ( Esther 1:19 ) when the decree is proposed to repudiate and degrade her that she is called merely "Vashti." She also ( Esther 1:9 ) presides at the banquet for the women. It is evident, therefore, that in the palace of the women there was no higher personage than Vashti.

Kitto's Popular Cyclopedia of Biblial Literature [11]

Vash´ti (beauty), the wife of Ahasuerus, King of Persia, whose refusal to present herself unveiled before the compotators of the king led to her degradation, and eventually to the advancement of Esther [[[Ahasuerus; Esther]]]