one day

the daytime, during the day / a half day, half of a day

(rare) the first day of the month

all day, throughout the day, sunrise to sunset, all around the clock

all day

one day, 24 hours / the daytime, the period from dawn until dusk / (figuratively) a short period of time / one day, someday, an unspecified day / the first day of the month

(collective, chiefly attributive) Japan and China

the daytime, during the day / noon, midday

sun / daytime, daylight / day

the eighth day of the month / eight days