Cyrillic letter “Ukrainian-Belarusian i” or “izhei”, also formerly used in Russian before 1918
AI overview
"І/і" is a letter from the Cyrillic alphabet that looks like a straight vertical line with a dot above it, used in Ukrainian and Belarusian writing and historically in Russian before spelling reforms in 1918. It matters because it's a fundamental part of modern Ukrainian and Belarusian orthography, helping to distinguish these languages' written forms from Russian and from each other.
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Article
The dotted і (І і; italics: І і), also called decimal i (after its former numeric value) or soft-dotted i, is a letter of the Cyrillic script. It commonly represents the close front unrounded vowel /i/, like the pronunciation of ⟨i⟩ in English "machine". It is used in the orthographies of Belarusian, Kazakh, Khakas, Komi, Carpathian Rusyn and Ukrainian and quite often, but not always, is the equivalent of the Cyrillic letter і (И и) as used in Russian and other languages. It was also used in Russian before the spelling reform of 1918.
In Ukrainian, the dotted і is the twelfth letter of the alphabet and represents the sound [i] in writing. Ukrainian uses и to represent the sound [ɪ]. In Belarusian, the dotted i is the tenth letter of the alphabet. It represents [i]. The two Carpathian Rusyn standard varieties use і, и and ы for three different sounds: /i/, /ɪ/ and /ɨ/, respectively. In Komi, і occurs solely after the consonants д, з, л, н, с, and т and does not palatalize them, while и does. In Kazakh and Khakas, і represents /ɘ/.