Ayin (also ayn or ain; transliterated ⟨ʿ⟩) is the sixteenth letter of the Semitic abjads, including Phoenician ʿayin Phoenician ayin.svgHebrew ʿayin עAramaic ʿē Ayin.svgSyriac ʿē ܥ, and Arabic ʿayn ع‎ (where it is sixteenth in abjadi order only).[note 1]

The letter represents a voiced pharyngeal fricative (/ʕ/) or a similarly articulated consonant. In some Semitic languages and dialects, the phonetic value of the letter has changed, or the phoneme has been lost altogether (thus, in Modern Hebrew it is reduced to a glottal stop or is omitted entirely).

The Phoenician letter is the origin of the Greek, Latin and Cyrillic letter O.