Ides
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
A division of time among the Romans. In March, May, July, and October, the Ides were on the 15th of the month; in the remaining months, on the 13th. This method of reckoning is stlll retained in the chancery of Rome, and in the calendar of the breviary.
Wharton.