E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The first of every month was so called by the Romans. Varro says the term originated in the practice of calling together or assembling the people on the first day of the month, when the pontifex informed them of the time of the new moon, the day of the nones, with the festivals and sacred days to be observed. The custom continued till A.U.C. 450, when the fasti or calendar was posted in public places. (See GREEK CALENDS.)