Yom Kip·pur (yôm? k?p??r, y?m?, y?m?, yôm? k?-po?or?)n. 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.[Hebrew yôm kippûr : yôm, day; see ywm in Semitic roots + kippûr, atonement (from kipp?r, to cover, atone; see kpr in Semitic roots).]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.Yom Kippur (j?m ?k?p?; Hebrew j?m ki?pur) n (Judaism) an annual Jewish holiday celebrated on Tishri 10 as a day of fasting, on which prayers of penitence are recited in the synagogue throughout the day. Also called: Day of Atonement [from Hebrew, from y?m day + kipp?r atonement]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014Yom Kip?pur (y?m ?k?p ?r, yo?m; Heb. ?y?m ki?pur) n. the holiest Jewish holiday, observed on the 10th day of Tishri by fasting and by recitation of prayers of repentance in the synagogue. Also called Day of Atonement. [