Mid-month date (4)
I believe the answer is:
ides
'mid-month date' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ides that I've seen before include "Julius Caesar died in these March days" , "Caesar was warned to beware the ones of March" , "March 15; dies (anag.)" , "Unlucky day for Julius Caesar" , "Julius Caesar was killed during the . . . . of March" .)