Omicron is the fifteenth letter of the Greek alphabet. This letter is derived from the Phoenician letter ayin: . In classical Greek, omicron represented the close-mid back rounded vowel IPA: [o] in contrast to omega which represented the open-mid back rounded vowel IPA: [ɔː] and the digraph ου which represented the long close-mid back rounded vowel IPA: [oː]. In modern Greek, both omicron and omega represent the mid back rounded vowel IPA: [o̞] or IPA: [ɔ̝]. Letters that arose from omicron include Roman O and Cyrillic O. The word literally means "little O" as opposed to "great O". In the system of Greek numerals, omicron has a value of 70.