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" or rule. The forms of the Cyrillic letter U are similar to the lowercase of the Latin letter Y (Y y; Y y).
APFM-1 training mine, distinguishable from the live version by the presence of the letter У (short for учебный, uchebnyy, "for training").U, from Alexandre Benois' 1904 alphabet book. It shows Ulitsa (street) and uraganʺ (hurricane).
History
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/. Later, the o was removed, leaving the modern upsilon-only form.
Consequently, the form of the letter is derived from Greek upsilon⟨Υ υ⟩, which was parallelly also taken over into the Cyrillic alphabet in another form, as Izhitsa⟨Ѵ⟩. (The letter Izhitsa was removed from the Russian alphabet in the orthography reform of 1917/19.)
It is normally romanised as "u", but in Kazakh, it is romanised as "w".
In certain languages, U is used to mark labialization.
Related letters and other similar characters
Similarity with Y (uppercase): The grapheme on the left is clearly a Cyrillic U, the one in the middle may represent both letters, the one on the right is clearly a Greek or Latin Y.
^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 (indu, ' nu, lu, gu, hu, zu, ru, etc. but not buormu)