ides

Today is the Ides of March, the day Julius Caesar was assassinated in 44 BC.
The term "ides" comes from the Latin iduare, "to divide." It refers to the midpoint of a month, which was supposed to coincide with the full moon. The Romans used the term to number a month's days (so the 13th of the month would be "two days before the Ides"), but otherwise there was no particular significance to the date.