The word "calendar" can be traced back to its Latin origin. It is derived from the Latin word "calendae", which referred to the first day of each month in the ancient Roman calendar. The Latin term "calendae" itself derived from the verb "calare", meaning "to announce" or "to call out", as the priests in ancient Rome would announce the new moon and the days of the month in public. Over time, the word "calendae" evolved into "calendarium", which referred to an account book or a register, and eventually gave rise to the English word "calendar" as we use it today.