IDES

A word occurring in the Roman calendar, inserted in all correct editions of the Prayer Book. The ides were eight days in each month: in March, May, July, and October, the ides ended on the 15th, and in all other months, on the 13th day. The word Ides, taken from the Greek, ( ειἶδος ,) means an aspect or appearance, and was primarily used to denote the full moon. The system of the original Roman calendar was founded on the change of the moon, the nones being the completion of the first quarter, as the ides were of the second.— Stephens, Book of Common Prayer; Notes on the Calendar.