n. 1 expiation; reparation for a wrong or injury. 2 the reconciliation of God and man. the Atonement the expiation by Christ of mankind's sin. Day of Atonement the most solemn religious fast of the Jewish year, eight days after the Jewish New Year.
[ at one + -MENT, after med.L adunamentum and earlier onement f. obs. one (v.) unite ]