(often capitalized) The notional first-quarter day of a Roman month, occurring on the 7th day of the four original 31-day months (March, May, Quintilis or July, and October) and on the 5th day of all other months.
The third day before the nones of March is March 5th; the third nones of August is August 3rd; and the third of the nones of November is November 3rd.