Mid-month day (4)
I believe the answer is:
ides
'mid-month day' 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's unlucky day in March" , "Mid-month date in Roman calendar" , "mid-month for the Romans" , "ill-fated time" , "Day in Roman months" .)