Its graphic form has remained fairly constant from Phoenician times until today.
The name of the Phoenician letter was ʿeyn, meaning "eye", and indeed its shape originates simply as a drawing of a human eye (possibly inspired by the corresponding Egyptian hieroglyph, c.f. Proto-Sinaitic script).
Its original sound value was that of a consonant, probably [ʕ], the sound represented by the cognate Arabic letter letter ع ʿayn.
The use of this Phoenician letter for a vowel sound is due to the early Greek alphabets, which adopted the letter as O "omicron" to represent the vowel /o/.
The letter was adopted with this value in the Old Italic alphabets, including the early Latin alphabet.
In Greek, a variation of the form later came to distinguish this long sound (Omega, meaning "large O") from the short o (Omicron, meaning "small o"). Greek omicron gave rise to the corresponding Cyrillic letter O and the early Italic letter to runic runic ᛟ.
Even alphabets constructed "from scratch", i.e. not derived from Semitic, usually have similar forms to represent this sound, e.g.; the creators of the Afaka and Ol Chiki scripts, each invented in different parts of the world in the last century, both attributed their vowels for 'O' to the shape of the mouth when making this sound.[original research?]
