Day originally marked by a full moon in the early Roman calendar (4)

I believe the answer is:

ides

(Other definitions for ides that I've seen before include "(In March) Caesar's time to beware" , "For example, March 15 in the Roman calendar" , "Eg March 15" , "Unlucky day for Julius Caesar" , "Julius Caesar's unlucky day in March" .)

I've seen this clue in The New York Times.

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