O, or o, is the fifteenth letter and the fourth vowel letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide.
O, the fourth vowel of the modern alphabet, corresponding to the Semitic ayin, which represented a breathing and not a vowel. The Semitic form may have derived from an earlier sign representing an eye.
O, o (oʊ) n., pl. O's Os, o's os oes. 1. the 15th letter of the English alphabet, a vowel. 2. any spoken sound represented by this letter.