Calendar (noun)

1. A system of organizing and measuring time, usually divided into days, weeks, months, and years.
2. A chart or document displaying such a system of organizing and measuring time.
3. A list of planned events or appointments.

Origin:

The word "calendar" comes from the latin word "calendarium" which means account book. it was first used in english in the 14th century.

Examples:

1. I use a digital calendar to keep track of my appointments.
2. The Mayan calendar was based on a combination of solar and lunar cycles.
3. She used a wall calendar to mark important dates.
4. The company releases its fiscal calendar at the beginning of each year.
5. I'll have to check my calendar before I can commit to a meeting.