ides (īdz) pl.n.
(used with a sing. or pl. verb) The 15th day of March, May, July, or October or the 13th day of the other months in the ancient Roman calendar.
[Middle English, from Old French, from Latin Īdūs.]
(pl.) c.1330, "middle day of a Roman month," from Fr. Ides (12c.), from L. idus "the eighth day after nones," a word perhaps of Etruscan origin. The 15th of March, May, July, and October; the 13th of other months.