one of the Jewish High Holidays, the Day of Atonement, a fast day of repentance during which the prayers recited include the Kol Nidre, observed on the 10th day of Tishri: Lev. 16:29-34
See Yom Kippur in American Heritage Dictionary 4
(yômˌ kĭpˈər, yōmˌ, yŏmˌ, yômˌ kē-po͝orˈ)
noun Judaism
A holy day observed on the tenth day of Tishri and marked by fasting and prayer for the atonement of sins. Also called Day of Atonement.