Ides

[ahydz] /aɪdz/

noun, (used with a singular or plural verb)
1.
(in the ancient Roman calendar) the fifteenth day of March, May, July, or October, and the thirteenth day of the other months.
1.
a Greek plural suffix appearing in scientific names:
cantharides.
/aɪdz/
noun
1.
(functioning as sing) (in the Roman calendar) the 15th day in March, May, July, and October and the 13th day of each other month See also calends, nones
n.

(plural) early 14c., “middle day of a Roman month,” from Old French Ides (12c.), from Latin idus (plural), a word perhaps of Etruscan origin. The 15th of March, May, July, and October; the 13th of other months. “Debts and interest were often payable on the ides” [Lewis].