Other forms: calendars
A calendar is the chart of all the days and months of the year. A wall calendar, mark the calendar, calendar year.
The one in use across most of the world is the Gregorian, adopted from 1582 to correct a drift in the older Julian one — Britain changed in 1752 and lost eleven days doing it. Note the spelling with an a in the middle; and that the Latin calendae was the first day of the month, when debts fell due.
1nouncalendarA chart of the days and months of the year.
“I've written her birthday on the calendar in the kitchen.”
calendar is a chart of time.
Latin calendarium was an account book, from calendae, the first day of the month, when debts were called in.
Middle English
kalender
English, today
calendar
Built from
From Middle English kalender. From Middle English kalender, from Old French calendier, from Latin calendarium (“account book”), from kalendae (“the first day of the month”), from kalō (“to announce solemnly, to call out (the sighting of the new moon)”), from Proto-Indo-European kelh₁-. a doublet of calendarium. Displaced native rīmbōc and ġerīmbōc.
Etymology from Wiktionary, CC BY-SA