noun
January; 13th month
Playful or poetic term for January, treating it as the 13th month of the previous year. Often used in contexts like New Year's greetings or when emphasizing the continuation of the old year. Compare with 正月 (New Year).
See also: 正月
あけましておめでとう。今年も十三月がやってきたね。
Happy New Year. The 13th month has come again this year, hasn't it?
十三月の寒さはまだまだ続く。
The cold of the 13th month continues.
正月 refers specifically to the New Year period (January 1st to 3rd or 7th), while 十三月 is a whimsical way to refer to the entire month of January as an extension of the old year.
Literally 'thirteenth month', a playful coinage treating January as a continuation of the previous year's calendar. The exact origin is uncertain, but it is used in modern Japanese for poetic or humorous effect.