ides
Concise Oxford English Dictionary © 2008 Oxford University Press:
ides /ʌɪdz/
▶plural noun (in the ancient Roman calendar) a day falling roughly in the middle of each month (the 15th day of March, May, July, and October, and the 13th of other months) from which other dates were calculated.
– origin OE: from OFr., from L. idus (pl.).
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