In current usage, the English word noon refers to midday, the time when the sun reaches the meridian.
Look into the etymology of the word noon, and you will find that it comes from the Latin word for the number nine.
So why does our word for the time when both hands of the clock are on the twelve come from a word for nine?
Like the word noon itself, the original time-related meaning goes back to the Romans. They counted the hours of the day from sunrise. The “ninth hour” (nona hora) was about 3 p.m. our time.
Christians adopted Jewish customs of praying at certain hours. When Christian monastic orders were formed, a daily timetable was drawn up centered on hours for prayer.
According to the earliest schedules, the monks were required to pray at three-hour intervals: 6-9 p.m., 9 p.m.-midnight, midnight-3 a.m., and 3 a.m.-6 a.m. The prayers to be said at specified times during the day are known as the Divine Office and the times at which they are to be recited are the canonical hours:
Prime: 6 a.m. “first hour”
Terce: 9 a.m. “third hour”
Sext: noon “sixth hour”
None: 3 p.m. “ninth hour”
Compline: before bed
Vigils was also known as the “Night Office.” Matins and Lauds originally referred to the prayers sung at dawn. In time, the Night Office came to be called Matins.
The shift in the meaning of noon from “3 p.m.” to “12 noon” began in the 12th century when the prayers said at the “ninth hour” were set back to the “sixth hour.”
By the year 1140, the Old English word non had taken on the meaning of “midday” or “midday meal.”
Like our words September, October, November, and December, noon is a fossil word that embeds customs of former ages.