hegira

n. [ Written also hejira. ] [ Ar. hijrah flight. ] The flight of Mohammed from Mecca, September 13, a. d. 622 (subsequently established as the first year of the Moslem era); hence, any flight or exodus regarded as like that of Mohammed. [ 1913 Webster ]

☞ The starting point of the Era was made to begin, not from the date of the flight, but from the first day of the Arabic year, which corresponds to July 16, a. d. 622. [ 1913 Webster ]