The letter originates from the letter izhitsa with a breve (Іереѵ̆ская власть, пучина Егеѵ̆ская, etc.) used in certain Ukrainian books at the end of the 16th and the beginning of the 17th centuries.
For Belarusian, the combination of the Cyrillic letter U with a breve was proposed by P.A. Bessonov in 1870 [REF].