Fateful March date (4)
I believe the answer is:
ides
'fateful march date' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ides that I've seen before include "Unlucky day for Julius Caesar" , "Day in Roman months" , "Fateful day for Caesar" , "March day fatal to Julius Caesar" , "date for 21 [ROMAN]?" .)