Definition of "day" in English

noun

1. The time when the Sun is above the horizon and it lights the sky.

   • day and night;  I work at night and sleep during the day.

2. A period of time equal or almost equal to a full day-night cycle, being 24 hours long.

   • Holonyms: week < megasecond < fortnight < month < year < gigasecond < century < kiloannum, kiloyear, millennium < terasecond < mega-annum, megayear < petasecond < giga-annum, gigayear < exasecond < zettasecond < yottasecond < ronnasecond < quettasecond
   • Meronyms: quectosecond < rontosecond < yoctosecond < zeptosecond < attosecond < femtosecond < picosecond < nanosecond < microsecond < millisecond < centisecond < decisecond < second < decasecond < minute < hectosecond < kilosecond < hour
   • I've been here for two days and a bit.

3. (informal or meteorology) A 24-hour period beginning at 6am or sunrise.

   • Your 8am forecast: The high for the day will be 30 and the low, before dawn, will be 10.

4. A period of time between two set times which mark the beginning and the end of day in a calendar, such as from midnight to the following midnight or (Judaism) from nightfall to the following nightfall.

   • The day begins at midnight.
   • Monday is the first day of the week in many countries of the world.

5. (astronomy) The rotational period of a planet.

   • A day on Mars is slightly over 24 hours.

6. The part of a day period which one spends at one’s job, school, etc.

   • I worked two days last week.

7. An observance lasting for a day, such as an annual holiday.

   • Christmas Day
   • Remembrance Day

8. A specified time or period; time, considered with reference to the existence or prominence of a person or thing; age; time; era.

   • every dog has its day; in that day; back in the day; in those days

9. A period of contention of a day or less.

   • The day belonged to the Allies.

verb

1. (rare, intransitive) To spend a day (in a place).