Ο/ο

Omicron (, ; uppercase Ο, lowercase ο, ) is the fifteenth letter of the Greek alphabet. This letter is derived from the Phoenician letter ayin: 16px|class=skin-invert. In classical Greek, omicron represented the close-mid back rounded vowel in contrast to omega, which represented the open-mid back rounded vowel , and the digraph which represented the long close back rounded vowel . In modern Greek, both omicron and omega represent the mid back rounded vowel . Letters that arose from omicron include Roman O and Cyrillic O and Ю. The name of the letter was originally ( ), but it was later changed to ( 'small o') in the Middle Ages to distinguish the letter from omega , whose name means 'big o', as both letters had come to be pronounced . In modern Greek, its name has fused into (). In the system of Greek numerals, it has a value of 70.

==Use== In addition to its use as an alphabetic letter, omicron is occasionally used in technical notation, but its use is limited since both upper case and lower case (Ο ο) are indistinguishable from the Latin letter "o" (O o) and difficult to distinguish from the Arabic numeral "zero" (0).