U (У у; italics: У у) is a letter of the Cyrillic script. It commonly represents the close back rounded vowel/u/, somewhat like the pronunciation of ⟨oo⟩ in "boot". The forms of the Cyrillic letter U are similar to the lowercase of the Latin letter Y (Y y; Y y), but like most other Cyrillic letters, the upper and lowercase forms are similar in shape and differ mainly in size and vertical placement.
Historically, Cyrillic U evolved as a specifically East Slavic short form of the digraph ⟨оу⟩ used in ancient Slavic texts to represent /u/. The digraph was itself a direct loan from the Greek alphabet, where the combination ⟨ου⟩ (omicron-upsilon) was also used to represent /u/.
^However, many Dungan books are set using Ӯ, with macron, instead of Ў, with breve, like the Dungan-Russian dictionary (1968). There is no ambiguity since it is the only У-with-a-diacritic in Dungan. It is used in Dungan syllables for which pinyin would use -u except in those with labial consonants (in du, ' nu, lu, gu, hu, zu, ru, etc. but not bu or mu)