Lewis & Short

Nōnae, ārum, f. [nonus], the fifth day in every month of the year, except March, May, July, and October, in which it was the seventh; the nones, so called because it was the ninth day before the ides, Varr. L. L. 6, § 28 Müll.: o Nonae illae Decembres, Cic. Fl. 40, 102: Nonis Februariis si Romae fuit, id. Quint. 18, 57: a. d. tertium Non. Januar. si agere coepisset, id. Fam. 5, 2, 8. After the expulsion of the kings, the marketdays were no longer allowed to fall on the nones, because the people celebrated the nones as the birthday of Servius Tullius, and fear was entertained of a movement on that day in favor of royalty, Macr. S. 1, 13. No wedding took place either on the nones or on the ides, because the following day was a dies ater, unfavorable for the offering to be made by the bride, id. ib. 1, 16. Augustus, for superstitious reasons, avoided undertaking any thing on the nones, Suet. Aug. 92.