As a day of the Roman calendar, via nōnae from the original Roman practice of counting forward to the next full or new crescent moon, the nones' occurrence 8 days before the ides of every month (9 counting inclusively) following the establishment of a fixed calendar, and from the Latin practice of treating most recurring calendrical days as plurals. Some scholars believe the name is a variant of the nundines (nūndinae fēriae), the Roman market days held every eight days (9 counting inclusively), which were likely announced for each coming month by the Roman kings on the first-quarter days.
As a time of day, via the plural form of Middle English, Anglo-Norman, & French none and Latin nōna after the manner of earlier matins, vespers, etc. As a meal, from the time of day, whether from its plural, genitive, or the occasional adverbial sense of -s.