Historical typefaces (like poluustav (semi-uncial), a standard font style for the Church Slavonic typography) and old manuscripts represent several additional glyph variants of Cyrillic O, both for decorative and orthographic (sometimes also "hieroglyphic"[1]) purposes, namely:
broad variant (Ѻ/ѻ), used mostly as a word initial letter (see Broad On for more details);
narrow variant, being used now in Synodal Church Slavonic editions as the first element of digraph Oy/oy (see Uk (Cyrillic) for more details), and in the editions of Old Believers for unstressed "o" as well;
variant with a cross inside (Crossed O), Ꚛ, used in certain manuscripts as the initial letter of words окрестъ 'around, nearby' (the root of this Slavonic word, крест, means 'cross') and округъ 'district, neighbourhood' with their derivatives;
"eyed" variant (Monocular O) with a dot inside (Ꙩ/ꙩ), used in certain manuscripts in spelling of word око 'eye' and its derivatives. In many other texts, including the birchbark letters, the monocular O was not used as a hieroglyph but largely as a synonym of Broad On signalling the word-initial position;
"two-eyed" variants (Binocular O) with two dots inside (Ꙫ/ꙫ or Ꙭ/ꙭ), also double "O" without dots inside were used in certain manuscripts in spelling of dual/plural forms of the words with the same root 'eye';
"many-eyed" variant (Multiocular O), ꙮ, used in certain manuscripts in spelling of the same root when embedded into word многоочитый 'many-eyed' (an attribute of seraphim).
InRussian, O is used word-initially, after another vowel, and after non-palatalized consonants. Because of a vowel reduction processes, the Russian /o/ phoneme may have a number of pronunciations in unstressed syllables, including [ɐ] and [ə].
