Fifteenth letter in the Greek alphabet
Omicron (, ;[1] uppercase Ο, lowercase ο, Greek: όμικρον) 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|Ю (Cyrillic)|Ю. The word literally means "little O" (o mikron) as opposed to "great O" (ō mega).[2] In the system of Greek numerals, omicron has a value of 70.
. 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|Ю (Cyrillic)|Ю. The word literally means "little O" (o mikron) as opposed to "great O" (ō mega).[2] In the system of Greek numerals, omicron has a value of 70.