Taisiya

Taisiya comes from the Greek Θαισις (Thaisis), which - rather than a variant of Thaïs - is probably a corruption of Ταησις (Taesis), a hellenization of the Coptic name Ⲧⲁⲏⲥⲉ. That name is ultimately derived from ancient Egyptian Tȝ-Is.t or Ta-Ỉs.t meaning "belonging to Isis".

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At least one Russian source states that Ⲧⲁⲏⲥⲉ was the original name of saint Thaïs of Alexandria, who is known as Taisiya in Russia and is the inspiration behind the use of the name there. Given the similarities between Taesis (which is Taisis in modern Greek) and the authentic Greek name Thaïs, it is understandable that the two names were often confused with each other, eventually resulting in Thaïs becoming the mainstream name for the saint (at least in the English-speaking world).

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Also compare these hellenized Coptic names, which are listed on this page: https://www.trismegistos.org/nam/list_all.php?selection=T&p=51: Thais, Thaisais, Thaisaridion, Thaisas, Thaisithis and Thaisous.

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Notable sources:

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- https://www.trismegistos.org/nam/detail.php?record=1237 (in English; this is about the name Taesis)
- https://ru.wikipedia.org/wiki/%D0%A2%D0%B0%D0%B8%D1%81%D0%B8%D1%8F (in Russian; this is about the name Taisiya and mentions the Coptic origin of the name)
- http://kurufin.ru/html/Rus_names/rus_t-u.html (in Russian; look for "Thais (Thaisis)" in one of the columns on the right)
- http://kurufin.ru/html/Translate/Thais.html (in Russian; this is about the name Taisiya)
- https://imya.com/name/14270 (in Russian; this is about the name Taisiya)
- https://heraldry.sca.org/names/paul/t-u.html (in English; see the entry for Taisiia)
- https://ru.wikipedia.org/wiki/%D0%A2%D0%B0%D0%B8%D1%81%D0%B8%D1%8F_%D0%95%D0%B3%D0%B8%D0%BF%D0%B5%D1%82%D1%81%D0%BA%D0%B0%D1%8F_%D0%A4%D0%B8%D0%B2%D0%B0%D0%B8%D0%B4%D1%81%D0%BA%D0%B0%D1%8F (in Russian; this is about saint Thaïs of Alexandria)

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As for the authentic Greek name Thaïs, it appears that this is usually written as Таис (Tais) in Russian. For example, see the Russian version of the Wikipedia article about the famous Greek hetaera that accompanied Alexander the Great on his campaigns: https://ru.wikipedia.org/wiki/%D0%A2%D0%B0%D0%B8%D1%81 (in Russian).

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It is interesting, though, that Tais is the Russian form and not Taida, because Greek -ais usually becomes -aida in Russian. See the following examples:

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- Athenais becomes Афинаида (Afinaida) in Russian: https://ru.wikipedia.org/wiki/%D0%90%D1%84%D0%B8%D0%BD%D0%B0%D0%B8%D0%B4%D0%B0_%D0%A4%D0%B8%D0%BB%D0%BE%D1%81%D1%82%D0%BE%D1%80%D0%B3%D0%B8%D1%8F_II
- Herais (also Irais) becomes Ираида (Iraida) in Russian: https://ru.wikipedia.org/wiki/%D0%98%D1%80%D0%B0%D0%B8%D0%B4%D0%B0_%D0%90%D0%BB%D0%B5%D0%BA%D1%81%D0%B0%D0%BD%D0%B4%D1%80%D0%B8%D0%B9%D1%81%D0%BA%D0%B0%D1%8F
- Ptolemais becomes Птолемаида (Ptolemaida) in Russian: https://ru.wikipedia.org/wiki/%D0%9F%D1%82%D0%BE%D0%BB%D0%B5%D0%BC%D0%B0%D0%B8%D0%B4%D0%B0_%D0%9A%D0%B8%D1%80%D0%B5%D0%BD%D1%81%D0%BA%D0%B0%D1%8F
- Zenais becomes Зинаида (Zinaida) in Russian: https://en.wikipedia.org/wiki/Zenaida (in English; lists the Russian form)

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Finally, variant transcriptions of the name Taisiya include Taisia, Taisiia and Taisija.