. . . . . . . . "Tau (uppercase \u03A4, lowercase \u03C4; Greek: \u03C4\u03B1\u03C5 [taf]) is the 19th letter of the Greek alphabet. In the system of Greek numerals it has a value of 300.The name in English is pronounced /ta\u028A/ or /t\u0254\u02D0/, but in modern Greek it is [taf]. This is because the pronunciation of the combination of Greek letters \u03B1\u03C5 has changed from ancient to modern times from one of [au] to either [av] or [af], depending on what follows (see Greek orthography).Tau was derived from the Phoenician letter taw 20px."@en .