a system of timekeeping that defines the beginning and length and divisions of the year
"The astronomer explained how our current calendar was adjusted to align perfectly with the Earth's orbit around the sun."
a list or register of events (appointments or social events or court cases etc)
"I have you on my calendar for next Monday"
a tabular array of the days (usually for one year)
"I checked my wall calendar to see what day next month's meeting falls on."
Any system by which time is divided into days, weeks, months, and years.
"The ancient Egyptian calendar was based on the cycles of the Nile River rather than the position of stars."
In plain English: A calendar is a schedule that shows the days, weeks, and months of a year so you can keep track of dates and events.
"She checked her calendar to see when her next meeting was scheduled."
Usage: Use "calendar" to refer to the specific chart or schedule displaying dates, not the general abstract system of timekeeping. It is incorrect to say "the calendar system" when you simply mean the monthly grid used for planning.
enter into a calendar
"The court clerk entered the settlement agreement into the official calendar to ensure it was heard at the next hearing."
To set a date for a proceeding in court, usually done by a judge at a calendar call.
"The judge moved to calendar the motion for next Tuesday during the morning session's calendar call."
In plain English: To calendar something means to officially schedule it for a specific date on your agenda.
"I will calendar that meeting for next Tuesday to make sure we have time to prepare."
Usage: As a verb, to calendar means to officially schedule or set a specific date for a legal proceeding or event. Judges typically use this term when they add a case to the court's docket during a formal calendar call.
The word "calendar" comes from the Latin kalendae, which referred to the first day of the month when the new moon was announced. It entered Middle English via Old French as a term for an account book, eventually evolving to mean the schedule of days we use today.