1) the day, used of the natural day, or the interval between sunrise and sunset, as distinguished from and contrasted with the night
1a) in the daytime
1b) metaph., "the day" is regarded as the time for abstaining from indulgence, vice, crime, because acts of the sort are perpetrated at night and in darkness
2) of the civil day, or the space of twenty four hours (thus including the night)
2a) Eastern usage of this term differs from our western usage. Any part of a day is counted as a whole day, hence the expression "three days and three nights" does not mean literally three whole days, but at least one whole day plus part of two other days.
3) of the last day of this present age, the day Christ will return from heaven, raise the dead, hold the final judgment, and perfect his kingdom
4) used of time in general, i.e. the days of his life.