n. 1. In the ancient Roman calendar, the 15th day of March, May, July, or October; or the 13th of the other months.
“Beware the ides of March!” -A Soothsayer
In Case You’re Interested (and really, why else would you be here?)…
Ides is the term for a day at about the middle of each month. The ancient Roman calendar organized their months around a set of “markers,” of which the ides was one.
Why? Because the Romans apparently loved complicated ways of calculating the date. Also it was originally supposed to fall on the day of the full moon. Other marker days included the nones on the 5th or 7th of the month, and the kalends (guess which word we got from that one!) on the 1st.
(Side note: Can you have just one ide? Apparently not. The word is spelled the same for both singular and plural. Like fish.)
The word may or may not be related to iduare ‘to divide.’ You might say opinion is divided.
Caesar certainly was.