Any period of 24 hours.
I've been here for two days and a bit.
A period from midnight to the following midnight.
The day begins at midnight.
Rotational period of a planet (especially Earth).
A day on Mars is slightly over 24 hours.
The part of a day period which one spends at one’s job, school, etc.
I worked two days last week.
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.
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 of contention of a day or less.
The day belonged to the Allies.
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.
To spend a day (in a place).