Tau (uppercase Τ, lowercase τ; [taf])'s the 19th letter of the Greek alphabet. In the system of Greek numerals it's a value of 300. This letter in English's pronounced /taʊ/, but in Modern Greek, this letter's name's pronounced /taf/. This's because the pronunciation of the combination of Greek letters αυ has changed from ancient to modern times from one of /aʊ/ to either /av/ or /af/ (see Greek orthography). Letters that arose from tau include Roman T and Cyrillic… (More on Tau)