day

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The period of light between dawn and nightfall; the interval from sunrise to sunset.
• noun The 24-hour period during which the earth completes one rotation on its axis, traditionally measured from midnight to midnight.
• noun The period during which a celestial body makes a similar rotation.
• noun One of the numbered 24-hour periods into which a week, month, or year is divided.
• noun The portion of a 24-hour period that is devoted to work, school, or business.
• noun A 24-hour period or a portion of it that is reserved for a certain activity.
• noun A specific, characteristic period in one's lifetime.
• noun A period of opportunity or prominence.
• noun A period of time in history; an era.
• noun Period of life or activity.
• adjective Of or relating to the day.
• adjective Working during the day.
• adjective Occurring before nightfall.
• idiom (day after day) For many days; continuously.
• idiom (day in, day out) Every day without fail; continuously.
• idiom (one day) Someday.
• idiom (one of these days) Someday.
• idiom (one of those days) A difficult or trying day.
• idiom (these days) At present; nowadays.

from The Century Dictionary.

• To become day; dawn: same as daw.
• To put off from day to day; adjourn. See daying.
• noun Same as dey.
• noun The time during which the sun shines upon any specified point of the moon's surface: opposed to lunar night.
• noun The interval between two successive transits of the moon across the meridian: sometimes called tidal day.
• noun December 27. a festival observed in honor of St. John the evangelist and apostle.
• noun One of the compartments of a mullioned window.
• noun The period during which the sun is above the horizon, or shines continuously on any given portion of the earth's surface; the interval of light, in contradistinction to that of darkness, or to night; the period between the rising and the setting of the sun, of varying length, and called by astronomers the artificial day.
• noun Hence Light; sunshine.
• noun The whole time or period of one revolution of the earth on its axis, or the space of twenty-four hours; specifically, the interval of time which elapses between two consecutive returns of the same terrestrial meridian to the sun.
• noun A particular or regularly recurring period of twenty-four hours, assigned to the doing of some specified thing, or connected with some event or observance: as, settling-day; bill-day.
• noun Specifically— An anniversary; the particular day on which some event is commemorated: as, St. Bartholomew's day; a birthday; New Year's day.
• noun The regularly recurring period in each week set apart for some particular purpose, as for receiving calls, etc.
• noun Time. Specified interval or space of time: as, three years' day to do something; he was absent for a year's day.
• noun Time to pay; credit.
• noun Period of time.
• noun Appointed time; set period; appointment.
• noun Definite time of existence, activity, or influence; allotted or actual term of life, usefulness, or glory: as, his day is over.
• noun A time or period, as distinguished from other times or periods; age: commonly used in the plural: as, bygone days; the days of our fathers.
• noun A distance which may be accomplished in a day; a day's journey. See phrase below.
• noun The contest of a day; a battle or combat with reference to its issue or results: as, to carry the day.
• noun A long while; time of uncertain length.
• noun A day in turn; a fixed recurrent day.
• noun Nautical, the account or reckoning of a ship's course for twenty-four hours, from noon to noon.
• noun At an indefinite future time; on some day in the future.
• noun To-day: as, how are ye the day?

from the GNU version of the Collaborative International Dictionary of English.

• noun 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; -- also called daytime.
• noun 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.