Omicron is the 15th letter of the Greek alphabet. This letter is derived from the Phoenician letter ayin: . In classical Greek, omicron represented the sound in contrast to omega and ου. In modern Greek, both omicron and omega represent the mid back rounded vowel. 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.