in the Roman calendar: the 15th of March or May or July or October or the 13th of any other month
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.
plural of ide
Alternative form of ides: the notional full moon of a Roman month, used in Roman dating.