Day (noun)

1. A period of 24 hours as a unit of time, reckoned from one midnight to the next.
2. The time between sunrise and sunset, regarded as a unit of time.
3. A specified day of the week or the date on which an event takes place.

Origin:

Old english dæg, of germanic origin; related to dutch dag and german tag.

Examples:

1. Today is a beautiful day.
2. He works six days a week.
3. They will leave on the 15th day of June.
4. The days are getting shorter as winter approaches.
5. In ancient Rome, they counted days from the start of the month.