Hour (noun)

1. A period of time equal to one twenty-fourth of a day and night and divided into 60 minutes.
2. A specific point in time marked by the clock.

Origin:

Old english hār, of germanic origin; related to dutch uur and german stunde.

Examples:

1. It's three hours since we left.
2. I'll be back in an hour.
3. I'm working ten hours a day.
4. The meeting will last for an hour.
5. The clock struck the hour.