🔼The name Zethar in the Bible
The name Zethar occurs only once in the Bible. It's the name of one of seven eunuchs of king Ahasuerus of Persia, whom he ordered to retrieve queen Vashti from her quarters in order for him to parade her off (Esther 1:10). As the queen declined, her position became vacant and was subsequently filled by Hadassah, a.k.a. Esther. Esther 1:10
🔼Etymology of the name Zethar
The name Zethar appears to be a transliteration of the Persian name Zaitar (says BDB Theological Dictionary), but although the similarity is obvious, scholars widely disagree on what that Persian name might have meant. Suffice it to say that the name Zethar as spelled in Hebrew does not look like any word available in the Bible. It's quite possible that the word זתר (ztr) existed in Hebrew, but since it isn't incorporated in the Bible, it's impossible to estimate what the nam Zethar might have meant to a Hebrew audience.
For a meaning of the name Zethar, NOBSE Study Bible Name List reads Sacrifice. Jones' Dictionary of Old Testament Proper Names proposes Very Great. And BDB Theological Dictionary has Conqueror.