The letter ŭ is called non-syllabic u (romanised: u nieskładovaje) in Belarusian because it resembles the vowel u but forms no syllables.

Kilka słów o poezji prostego ludu tej naszej polskiej prowincji, o jego muzyce, śpiewie, tańcach was printed with û in Belarusian citations instead, but it was explained that the proper letter was u with Latin brevis.

The proper letter ŭ was first used in printing in 1845, in the novel Tajemnicze domino czyli Skutki niestałości by Gabriel Ossowski (in Polish with occasional Belarusian).

As in Belarusian, Esperanto Ŭ is pronounced as a non-syllabic [u̯], primarily in the diphthongs aŭ, eŭ and rarely oŭ.

It is thought that ŭ was created by analogy with the Belarusian letter ў (Cyrillic u with breve), which was proposed by P.A.

When ŭ was pronounced, it would follow a stressed vowel and stand in for semivowel u, as in words eŭ, aŭ, and meŭ, all spelled today without the breve.

Once frequent, it survives today in author Mateiu Caragiale's name – originally spelled Mateiŭ (it is not specified whether the pronunciation should adopt a version that he himself probably never used, while in many editions he is still credited as Matei).

In some philological transcriptions of Latin, "ŭ" denotes a short U — for example, "fŭgō" ([ˈfʊɡoː], to chase away), vs "fūmō" ([ˈfuːmoː], to smoke).