1.
eight days
A duration of eight days.
八日かかりました。
It took eight days.
八日間の旅行です。
It's an eight-day trip.
八日も待った。
I waited for eight days.
あと八日で終わる。
It will be finished in eight days.
八日ぶりに会った。
We met for the first time in eight days.
2.
the eighth (day of the month)
The eighth day of any month.
3月八日に届きます。
It will arrive on March 8th.
八日は会議があります。
There's a meeting on the 8th.
来月八日に届く。
It will arrive on the 8th of next month.
八日までに提出してください。
Please submit it by the 8th.
八日は予定がある。
I have plans on the 8th.
八日 uses native Japanese counting and means both "eight days" (duration) and "the 8th" (date).
USAGE:
- Duration: 八日かかる (takes eight days)
- Date: 八日に届く (arrives on the 8th)
- 八日間: eight-day period (adds 間 for explicit duration)
DAYS 1-10 (SPECIAL READINGS):
- 一日, 二日, 三日, 四日, 五日
- 六日, 七日, 八日, 九日, 十日
NOTE:
Days 11-31 use regular 十一日 pattern, except 二十日. The reading ようか applies only to 8, not 18 (十八日) or 28 (二十八日).