Often with initial capital: the first day of a month
‘The third day before the calends of February is 30 January, the third calends of March is 27 or 28 February, and the third of the calends of May is 29 April.’;
The notional full-moon day of a Roman month, occurring on the 15th day of the four original 31-day months (March, May, Quintilis or July, and October) and on the 13th day of all other months.
‘The third day before the ides of March is March 13th; the third ides of August is August 11th; and the third of the ides of November is November 11th.’;
the first day of a month of the Roman calendar.
The fifteenth day of March, May, July, and October, and the thirteenth day of the other months.
‘The ides of March remember.’;
(by extension) A day for settling debts and other accounts.
in the Roman calendar: the 15th of March or May or July or October or the 13th of any other month
(rare) nodot=1; (figuratively) an account, a record.
The first day of something; a beginning.
The first day of each month in the ancient Roman calendar.
The calends or kalends (Latin: kalendae) is the first day of every month in the Roman calendar. The English word calendar is derived from this word.