first month of the lunar calendar
Refers to the first month in the traditional Japanese lunar calendar, roughly corresponding to February in the modern calendar. Used in historical or poetic contexts.
In the old lunar calendar, Mutsuki is considered the beginning of spring.
Poetic or traditional name for January in the modern calendar, often used in literature, almanacs, or when giving a classical feel.
The cold of Mutsuki (January) is the harshest of the year.