''Beware the ... of March'' (Julius Caesar) (4)
I believe the answer is:
ides
(Other definitions for ides that I've seen before include "Julius Caesar was told to beware the . . . . of March" , "13th or 15th day of the month in Roman calendar" , "Side of March when Caesar died" , "Caesar was killed in this side of March" , "Mid-month day in the Roman calendar" .)