Both Latin o and Cyrillic о originated from Greek letter ο (omicron), which, in turn, was adopted from Phoenician alphabet. According to Wikipedia, the name of Phoenician letter 𐤏 was ʿayin, meaning “eye”, its shape was that of, well, an eye, and it was ultimately derived from the Egyptian hieroglyph 𓁹 ı͗r. (That is, “eye”.)
In many languages, o can constitute a whole word. For example, in Spanish, Italian, Catalan, Tagalog and Tok Pisin o is a conjunction meaning “or”. In Russian and some other Slavic languages, о (or o) is a preposition with a variety of meanings such as “about”, “of”, “on”, “against”, “upon”. In Scots, it is a preposition “of”. In Scottish Gaelic, “from”. In Welsh, both “of” and “from”. In Romanian, a feminine singular indefinite article. In Greek, ο is a masculine singular definite article. In Turkish, a pronoun “he”, “she”, or “it”. In Guaraní, it means “house”.
Oh! Almost forgot: in many, many languages o is an interjection. Meaning “oh” or “O”.
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