c.1420, in ref. to the Roman calendar, "ninth day before the ides of each month" (7th of March, May, July, October, 5th of other months), from L.
nonæ (acc.
nonas), fem. pl. of
nonus "ninth." Ecclesiastical sense of "daily office said originally at the ninth hour of the day" is from 1709; originally fixed at ninth hour from sunrise, hence about 3 p.m. (now usually somewhat earlier), from L.
nona (hora) "ninth (hour)," from fem. pl. of
nonus "ninth," contracted from
*novenos, from
novem "nine" (see
nine). Also used in a sense of "midday" (see
noon).