/day/ , n.
1. the interval of light between two successive nights; the time between sunrise and sunset: Since there was no artificial illumination, all activities had to be carried on during the day.
2. the light of day; daylight: The owl sleeps by day and feeds by night.
3. Astron.
a. Also called mean solar day . a division of time equal to 24 hours and representing the average length of the period during which the earth makes one rotation on its axis.
b. Also called solar day . a division of time equal to the time elapsed between two consecutive returns of the same terrestrial meridian to the sun.
c. Also called civil day . a division of time equal to 24 hours but reckoned from one midnight to the next. Cf. lunar day, sidereal day .
4. an analogous division of time for a planet other than the earth: the Martian day.
5. the portion of a day allotted to work: an eight-hour day.
6. a day on which something occurs: the day we met.
7. ( often cap. ) a day assigned to a particular purpose or observance: New Year's Day.
8. a time considered as propitious or opportune: His day will come.
9. a day of contest or the contest itself: to win the day.
10. Often, days . a particular time or period: the present day; in days of old.
11. Usually, days . period of life or activity: His days are numbered.
12. period of existence, power, or influence: in the day of the dinosaurs.
13. light 1 (def. 19a).
14. call it a day , to stop one's activity for the day or for the present; quit temporarily: After rewriting the paper, she decided to call it a day.
15. day in, day out , every day without fail; regularly: They endured the noise and dirt of the city day in, day out. Also, day in and day out .
[ bef. 950; ME; OE daeg; c. G Tag ]