- (astronomy) Rotational period of a planet (especially Earth).
"A day on Mars is slightly over 24 hours."
- A specified time or period; time, considered with reference to the existence or prominence of a person or thing; age; time.
"Every dog has its day."
- A period from midnight to the following midnight.
"The day begins at midnight."
- Part of a day period between sunrise and sunset where one enjoys daylight; daytime.
"day and night; I work at night and sleep during the day."
- Any period of 24 hours.
"I've been here for two days and a bit."
- The part of a day period which one spends at one’s job, school, etc.
"I worked two days last week."
- A period of contention of a day or less.
"The day belonged to the Allies."
- (rare) To spend a day (in a place).