| 1. | Astronomy. the time interval between two successive transits by the sun of the meridian directly opposite that of the observer; the 24-hour interval from one midnight to the following midnight. |
| 2. | Law. the period of time from sunrise to sunset. |
[dey] 
| 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. | Astronomy.
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| 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 initial capital letter) 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. |
| solar day n. A mean solar day. |