Its graphic form has remained fairly constant from Phoenician times until today.

The name of the Phoenician letter was ʿeyn, meaning "eye", and its shape originates simply as a drawing of a human eye (possibly inspired by the corresponding Egyptian hieroglyph, cf.

Before a noun, usually capitalized, it indicates direct address (the vocative case), as in the titles "O Canada" or "O Captain!

Derived letters such as ⟨ö⟩ and ⟨ø⟩ have been created for the alphabets of some languages to distinguish values that were not present in Latin and Greek, particularly rounded front vowels.

[citation needed] In the International Phonetic Alphabet, ⟨o⟩ represents the close-mid back rounded vowel.