O definition: the fifteenth letter of the English alphabet, a vowel. See examples of O used in a sentence. 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. This article lists things that start with o across foods, animals, colors, and more. By learning these words, readers can improve their vocabulary and strengthen recall of common categories. Learn the alphabet with Bob the Train in this fun and engaging Letter O Song featuring O for Owl and more! 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 - 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. O is used to mean zero, for example when you are telling someone a phone number, or mentioning a year such as 1908. 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. There are many systems of example words, including the NATO Phonetic Alphabet, but there are less formal systems as well. For example, Oscar might spell his name on the phone by saying O as in owl, S as in snake, C as in cat, A as in apple, and R as in rabbit. 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.