NEFASTI DIES, in Roman antiquity, an appellation given to those days wherein it was not allowed to administer justice, or hold courts. They were so called because, non fari licebat, the praetor was not allowed to pronounce the three solemn words or formulas of the law, do, dico, addico, I give, I appoint, I adjudge. These days were distinguished in the calendar by the letter N, for nefastus; or N. P. Nefastus Primo, when the day was only nefastus in the forenoon, or first part. The days of a mixed kind were called intercali.