also: いちじつ
noun, adverb
one day; a day
Refers to a single day as a unit of time or a specific day. Can be used adverbially.
一日に三回、薬を飲む。
I take the medicine three times a day.
この仕事は一日で終わる。
This work will be finished in one day.
adverb, noun
all day; the whole day; from morning till night
Only with reading いちにち
Emphasizes the entire duration of a day. Restricted to the reading いちにち.
昨日は一日中雨が降っていた。
It rained all day yesterday.
彼は一日働きづめだった。
He worked the whole day without a break.
noun
When read as ついたち, this meaning is standard. With the reading いちにち, it is less common and may be used in contexts like deadlines or schedules. See also １日 (ついたち).
See also: １日 (ついたち)
来月の一日が締め切りです。
The deadline is the first day of next month.