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

total concentration in something, being totally absorbed insomething

immersing oneself in something completely, totally absorbing oneself in something

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

work; operation