Noun
The first day of each month in the ancient Roman calendar.
Source: Webster's dictionaryThe days of these calendars were counted down (inclusively) to the next named day, so February 24 was ante diem sextum Kalendas Martias ("the sixth day before the calends of March") often abbreviated a. d. VI Kal. Source: Internet
The calends are always the first day of the month, and before Julius Caesar's reform fell sixteen days (two Roman weeks) after the ides (except the ides of February and the intercalary month). Source: Internet
New Shorter Oxford English Dictionary Latin calendarium meant "account book, register" (as accounts were settled and debts were collected on the calends of each month). Source: Internet