1.
three days
A duration of three days.
三日かかります。
It takes three days.
三日後に届きます。
It will arrive in three days.
三日も雨が続いた。
It rained for three days straight.
三日間の出張です。
It's a three-day business trip.
三日坊主で終わった。
It ended after just three days (gave up quickly).
2.
the third (day of the month)
The third day of any month.
1月三日に会いましょう。
Let's meet on January 3rd.
三日は忙しいです。
I'm busy on the 3rd.
来月三日に予約した。
I made a reservation for the 3rd of next month.
三日までに返事します。
I'll reply by the 3rd.
三日は空いていますか。
Are you free on the 3rd?
三日 has two meanings: a duration of three days, and the 3rd day of the month. Context usually makes the meaning clear.
DAYS OF THE MONTH (1-10):
- 一日, 二日, 三日, 四日, 五日
- 六日, 七日, 八日, 九日, 十日
COMMON EXPRESSIONS:
- 三日間: three days (with counter)
- 三日後: three days later
- 三日前: three days ago
IDIOM:
三日坊主 literally "three-day monk" means someone who gives up easily or lacks perseverance. Used when someone starts something but quickly abandons it.