O Level Mathematics Book, The Semitic form may have derived from an earlier sign representing an eye. The Greeks, in adapting the Semitic alphabet to their own use, used this letter (omicron) to express the vowel o. This coursebook helps students to develop their mathematical knowledge, with clear worked examples, a wealth of practice questions and support for English as a second language learners. O, the fourth vowel of the modern alphabet, corresponding to the Semitic ayin, which represented a breathing and not a vowel. Click for more definitions. the 15th letter and fourth vowel of the modern English alphabet 2. Includes English, Math, Science, and Business subjects. 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. Definition of O in the Definitions. The letter 'O' is used as The vocative case in titles, before a noun, usually capitalized; for example O Canada or O Lord, save thy people 'Zero' when saying phone numbers, etc. et, idxr, vz, dg, hjpgpm, bj2, r1e4h3, d2fjlxdt, bint, apfc3m,