Translation guide
A unit of time in the traditional Chinese and Japanese calendar, equal to 10 days, or a period of 10 days. Also used to refer to a decade of age (e.g., one's 30s).
Referring to a block of 10 days, especially in traditional calendars or when dividing a month into three parts.
The standard term for a 10-day period. A month is divided into 上旬 (first 10 days), 中旬 (middle 10 days), and 下旬 (last 10 or so days).
The new project will start in the first ten days of the month.
下旬にお会いしましょう。
Let's meet in the last part of the month.
Literally 'a period of ten days'. Used when specifying a duration rather than a calendar division.
十日間の休暇を取ります。
I'll take a ten-day vacation.
Referring to a ten-year range of a person's age, like 'in one's 30s'.
Attach to a number to indicate a decade of age. For example, 30代 means 'in one's 30s'. This is the most common way to express age decades.
彼は30代です。
He is in his thirties.
40代の女性が増えています。
The number of women in their forties is increasing.
Rarely used to mean a decade of age, mostly in literary or historical contexts. Not recommended for everyday use.
彼は八旬を迎えた。
He has reached his eighties.
旬 refers to a division of a month into three 10-day blocks (上旬, 中旬, 下旬). 十日間 simply means a duration of ten days, not tied to the calendar.
While 旬 can technically mean a decade of age, it sounds archaic. Use 〜代 instead.