In Asia, the seven-day week as a unit for regulating the cycle of work, rest, and business activities is a relatively recent import from the West, having been adopted in the 19th and 20th centuries. However, the roots of the names of the days go back much further.
1. The naming of the days of the week in Japanese and Vietnamese is based on Western models, although the models, dates, and routes of transmission are completely different. The Japanese names were transmitted via Buddhism, the Vietnamese names via Christianity.
a. The Japanese names, which follow the names of the sun, moon, and five inner planets, were brought to China from the ancient West (ultimately the ancient Middle East) in the 8th century as a part of Buddhist astrology, and then taken from China to Japan. In the 19th century, the Japanese found that these names that they had borrowed so long ago matched the names used in the modern Western languages, providing them with a ready-made set of names when adopting the Western week.
The Japanese names preserve the ancient Western planetary day names perfectly — much better, indeed, than the English ones. The problem with English is that the Germanic gods, unlike the Roman, Greek, and earlier gods, are not identified with the planets. By contrast, the Japanese names refer to the Sun, Moon, and the five planets. The only difference is that the planets in the Japanese week have Chinese names based on the 'Five Elements' rather than pagan gods.
b. The Vietnamese system is related to the Catholic liturgical naming system, which follows the traditional Christian order. The week starts on Sunday, the Lord's Day, followed by Monday as the second day, Tuesday the third day, Wednesday the fourth day, etc. The Vietnamese system appears to have been introduced by Portuguese missionaries in the 17th century. Thanks to these missionaries, the Vietnamese names follow the Portuguese names. The main differences are that Saturday is not called the Sabbath in Vietnamese, and the name of Sunday was subtly changed from 'Lord's Day' to 'Main Day' by the adherents of other religions.
The Portuguese were the only people in Europe to adopt the names of the days that the Church attempted to enforce among Christians in the West. Vietnamese is therefore more faithful than almost any modern European language to the preferred Catholic naming. And with the increasing trend to adopt Monday rather than Sunday as the first day of the week, Vietnamese and Portuguese now stand out as two of a small number of languages in the world to explicitly treat Sunday as the first day of the week.
2. The Chinese were familiar with the ancient planetary names that had come overland from the West with Buddhism. However, when the Western-style week came to China in modern times, ordinary people first associated it with Christian missionaries. A popular system of numbering the days arose from this encounter, starting from 'Sunday', the 'day of worship', followed by Monday (literally Worship One), Tuesday (Worship Two), etc. The word 'worship' (libai) thus came to mean 'week' and is still commonly used that way.
However, official practice is to replace libai with xingqi, a word meaning 'star period'. Xingqi is an unrelated word from ancient times that has been revived to mean 'weak'. It was chosen as a nod at the earlier Buddhist planetary names. A third word for 'week', zhou, which means 'cycle' and was originally introduced from Japanese, is also becoming popular. Whichever word is used for 'week', the system of numbering is the same in all cases.
Among the expressions used for naming the days of the week in the three CJV languages, libai 'worship' may be the only one that has genuinely arisen from common popular usage. All other naming systems have been imposed from above or introduced from elsewhere. Ironically, libai has failed to win official support and the more 'politically correct' xingqi is now favoured.
3. Mongolian originally borrowed the Tibetan and Indian planetary names for the days of the week (which the Indians themselves originally adopted under ancient influence from the west) due to the pervasive influence of Tibetan religion.
In everyday life, however, a system of numbering is used for the weekdays, and the days of the weekend are known as 'days of rest', from the Socialist era. A similar counting system used in Inner Mongolia clearly shows the influence of the Chinese names using xingqi, including the use of a nonsensical word for 'Sunday'. There is some possibility that the Mongolian and Inner Mongolian names originally had the same roots, although this requires further study.
In Buryat, a standardised dialect of Mongolian spoken in Russia, the numbering system differs from that of Mongolian proper by treating Sunday rather than Monday as the first day of the week. This system has no identifiable source. Russian names are also used in Buryatia.
Many points concerning the days of the week still need clarification. For
- The process by which the planetary names of the days of the week came to China is still not totally clear. When did they first arrive in China, and by what route?
- When and how did the Chinese adopt their current system? In particular, when and how did the word 'worship' come to mean 'week', and how did the numbering system come about?
- More information is needed on the transmission of the Catholic liturgical calendar to Vietnamese, in particular, concrete evidence for a Portuguese origin.
- What was the story behind the official adoption of the ancient planetary names for the days of the week in 19th century Japan?
Any leads or answers that could help resolve the above and any other questions would be gratefully received, with acknowledgement.