1. The time of light, or interval between one night and the next; the time between sunrise and sunset, or from dawn to darkness; hence, the light; sunshine.
  2. The period of the earth's revolution on its axis. -- ordinarily divided into twenty-four hours. It is measured by the interval between two successive transits of a celestial body over the same meridian, and takes a specific name from that of the body. Thus, if this is the sun, the day (the interval between two successive transits of the sun's center over the same meridian) is called a solar day; if it is a star, a sidereal day; if it is the moon, a lunar day. See Civil day, Sidereal day, below.
  3. Those hours, or the daily recurring period, allotted by usage or law for work.
  4. A specified time or period; time, considered with reference to the existence or prominence of a person or thing; age; time.
  5. (Preceded by the) Some day in particular, as some day of contest, some anniversary, etc.