Calendarian

Part of speech: noun

Definitions

1. A person who specializes in the study, computation or production of calendars ; someone devoted to observing the dates of religious or festival days
2. One skilled in constructing or reckoning calendars ; a person who strictly keeps track of and follows the schedule of feast days and observances
3. A specialist who designs or calculates calendars ; an individual who meticulously adheres to the timetable of festivals and holy days

Etymology: Calendarian has a simple build: "calendar" plus the agent suffix "-ian," the same ending found in "librarian" and "historian." "Calendar" itself came into English in the Middle Ages from Latin "kalendarium," an account book, and the Latin word traces back to "kalendae," the first day of each month. Roman creditors and debtors settled accounts on the Kalends, which is why the word for a book of dates ultimately tracks back to a day of payment. The noun "calendarian" is much later and far less common than "calendar" itself. It appears in English in the 1600s to describe someone who compiled or studied calendars, and in the 19th century it could also mean a writer of almanacs. Its scope has always been narrow, so you will mostly meet it in older dictionaries and antiquarian writing rather than everyday speech.