Protoslavic *kvě̑tъ from *kvisti 'to bloom, to blossom, to flower' from  Proto-Indo-European *ḱweyt- 'to shine' with irregular centumization. Per Derksen, from Proto-Indo-European *ḱweyt-, where Proto-Indo-European *ḱw- is depalatalized to *kw- in Balto-Slavic before a back vowel but has its regular reflex św- before a front vowel, and the complex pattern of related Proto-Slavic words with *kv- and *sv- (see Related terms, below) is due to analogical changes in both directions. Per Rix (LIV), there are two separate roots, Proto-Indo-European *ḱweyt- (“to become bright”) and Proto-Indo-European *kweyt- (“to shine”), the latter found only in Balto-Slavic. Chernykh refers to a substitution of "West-European" *k in place of *ḱ-, presumably suggesting a borrowing from a Centum language to the West of Proto-Balto-Slavic. Trubachev's theory is of "secondary centumization", which appears to be essentially the same as Chernykh's.

Черных 2, 362, Фасмер 4,292-293, Derksen 2008, 259. ЭССЯ 13, 167, Lexikon der indogermanischen Verben, 2nd edition, Wiesbaden: Dr. Ludwig Reichert Verlag, 340, 375

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