| Noun | 1. | major fast day - one of two major fast days on the Jewish calendar fast day - a day designated for fasting Day of Atonement, Yom Kippur - (Judaism) a solemn and major fast day on the Jewish calendar; 10th of Tishri; its observance is one of the requirements of the Mosaic law Fast of Ab, Fast of Av, Ninth of Ab, Ninth of Av, Tisha b'Ab, Tisha b'Av, Tishah b'Ab, Tishah b'Av - (Judaism) a major fast day on the Jewish calendar commemorating the destruction of the temples in Jerusalem |