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.]
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.
