Wikipedia
Nayrouz or Neyrouz is a feast when martyrs and confessors are commemorated within the Coptic Orthodox Church. Celebrated on September 11, the day is also the start of the Coptic new year and its first month, Thout.
The Feast of Neyrouz marks the first day of the Coptic year. Ignorant of the Egyptian language for the most part, the Arabs confused the Egyptian new year's celebrations, which the Egyptians called the feast of Ni-Yarouou (lit. the feast of the rivers), with the Persian feast of Nowruz, from which the word Nayrouz etymologically comes from. The misnomer remains today, and the celebrations of the Egyptian new year on the first day of the month of Thout are known as the Neyrouz. Its celebration falls on the 1st day of the month of Thout, the first month of the Egyptian year, which for AD 1901 to 2098 usually coincides with 11 September, except before a Gregorian leap year when it begins September 12.