day

day period of time for the earth to rotate once on its axis. The ordinary day, or solar day, is measured relative to the sun, being the time between successive passages of the sun over a stationary observer's celestial meridian . The length of a solar day varies during the course of a year, so for purposes of time measurement an average, or mean, solar day is used (see solar time ), equal to exactly 24 hr. The sidereal day, used by astronomers, is measured relative to the fixed stars rather than the sun (see sidereal time ); it is about 4 min shorter than the mean solar day. The term day is also used to refer to that part of each 24-hr period during which the sun's direct rays are not blocked by the earth, this period of daylight hours extending from sunrise to sunset; the remaining portion of the 24 hr is called night. If the plane of the earth's orbit about the sun coincided with the plane of the equator, day and night would each be 12 hr long everywhere on the earth all year long. However, because of the tilt of the earth's axis of rotation, the times of sunrise and sunset vary from day to day, with the result that in the Northern Hemisphere there are long days and short nights in the summer and short days and long nights in the winter. See equinox ; solstice .

day Jews in the NT period reckoned each day to start and finish at 6 p.m., and periods of the day were known by such general terms as morning or evening. Days of the week, except Sabbath, had no special names but were given numbers.

day as the day lengthens, so the cold strengthens proverbial saying, early 17th century, recording the tradition that the coldest weather arrives when days begin to grow lighter.
be the day weary or be the day long, at last it ringeth to evensong even the most difficult time will come to an end; saying recorded from the early 16th century.
day of reckoning the time when past mistakes or misdeeds must be punished or paid for, a testing time when the degree of one's success or failure will be revealed; with allusion to Judgement Day, on which (in some beliefs) the judgement of mankind is expected to take place.
day-star the morning star, (in poetic use) the sun; figuratively, someone or something regarded as the precursor of a new era.
don't give up the day job don't recklessly abandon steady work with the idea of making a fortune by pursuing a hobby or alternative interest. Used as a humorous way of recommending someone not to pursue an alternative (and perhaps more glamorous) career at which they are unlikely to be successful.

See also days, every dog has his day, make someone's day, a rainy day, red-letter day, Rome was not built in a day, tomorrow is another day, a year and a day.