calendarium

Calendarium is a Latin noun meaning calendar or a register of days and dates. It derives from calendae, the Kalends or the first day of the Roman month, with the suffix -arium forming a noun that denotes a collection or repository. The term is used in historical and manuscript contexts rather than contemporary everyday language.

Historically, calendaria were common in manuscript culture. In medieval and early modern Europe, a calendarium could be a calendar section embedded in a liturgical book, a standalone almanac, or a clerical record listing saints’ feast days, liturgical seasons, and civil or ecclesiastical dates. Some calendars recorded lunar phases, Epacts, and instructions for fasting and rites. Monastic libraries often preserved large calendaria that guided ritual cycles and the commemoration of patrons, martyrs, and notable church or civic figures.

Beyond liturgical use, the word could denote a general register or ledger used to record dates, obligations, or public events in Latin administrative contexts. In modern scholarship, calendarium is typically encountered in studies of medieval manuscripts, ancient or medieval religious calendars, or the history of timekeeping, and is usually distinguished from the everyday English term calendar.

In sum, calendarium reflects the long-standing role of calendars as tools for organizing religious, civic, and daily life in historical societies, expressed through Latin linguistic and manuscript traditions.