also: そうげつ
noun
eleventh month of the lunar calendar
Obsolete term for the eleventh month of the old lunar calendar, roughly corresponding to December in the modern calendar. Used in historical or literary contexts.
旧暦の霜月は、今の十二月にあたる。
The old lunar calendar's Shimotsuki corresponds to December in the modern calendar.
From 霜 (shimo, 'frost') + 月 (tsuki, 'month'), referring to the month when frost appears. The reading しもつき is a kun'yomi compound; そうげつ is the on'yomi reading.