last day of the year; New Year's Eve
Archaic term for New Year's Eve; in modern Japanese, 大晦日 (おおみそか) is the standard word. This form is now mostly encountered in historical or literary contexts.
See also: 大晦日
Long ago, people ate year-crossing soba on the night of New Year's Eve.
The spelling 大晦 can be found in classical literature.