O definition: the fifteenth letter of the English alphabet, a vowel. See examples of O used in a sentence. Accents placed on the letter O —such as Ó, Ò, Ô, Õ, and Ö —change pronunciation, meaning, or grammatical emphasis. Accented O has a unique sound, and its usage varies depending on the language and context. The letter O is the fifteenth letter in the English alphabet and is classified as a vowel. It has two primary sounds: the long O sound, which is like the /O/ in open, and the short O sound, which is like the /o/ in octopus. O (minuscule: 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 - Wiktionary, the free dictionary. Jump to content. Main menu. move to sidebarhide. Navigation. Main page. Community portal. Requested entries. Recent changes. Random entry. Help. Glossary. Contact us. Special pages. Search. Appearance. Donations. Create account. Log in. Personal tools. Donations. Create account. Log in. Contents. What do these words share in common? Children will learn that they begin with the letter O. Ó (minuscule: ó), known as O-acute, is a Latin-script character composed of the letter O and an acute accent. It is found in the Czech, Dobrujan Tatar, Emilian-Romagnol, Faroese, Hungarian, Icelandic, Kashubian, Polish, Slovak, Karakalpak, and Sorbian languages. This super-catchy and clear alphabet song also lets children hear the letter O sound and see each letter at the beginning of five simple words paired with colorful kid-friend images. 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. Learn all about the Letter O, with Jackson! Can you make the O sound? How many words do you know starting with the Letter O? Time to learn the alphabet!.