CALENDS

Any system by which time is divided into days, weeks, months, and years.

"The three principal calendars are the Gregorian, Jewish, and Islamic calendars."

A means to determine the date consisting of a document containing dates and other temporal information.

"Write his birthday on the calendar hanging on the wall."

A list of planned events.

"The club has a busy calendar this year."

Often with initial capital: the first day of a month

"The third day before the calends of February is 30 January, the third calends of March is 27 or 28 February, and the third of the calends of May is 29 April."

(by extension) A day for settling debts and other accounts.

(by extension) Synonym of Rosh Hodesh