Shaku is a narrow board held in the right hand when one wears sokutai (traditional ceremonial court dress) in Japan.
It originated in China where it is said to have been a board used by a government official for writing memos. Shaku was introduced from China in the sixth century, and it was first used in Japan during the Imperial Court ceremony, wherein a sequence of the ceremony was written down as memos on a piece of paper called shakugami pasted on the back of the shaku. Later shaku came to be used for giving a dignified air to the holder during important ceremonies and Shinto rituals.
There are two types of Shaku: geshaku which is made of ivory and mokushaku which is made of wood. Formerly, there was a rule according to which geshaku was used by persons of the Goi (Fifth Rank) or above, and mokushaku was used by persons of the Rokui (Sixth Rank) or below; later, however, geshaku came to be used during formal attire (court) and mokushaku in other occasions, regardless of the rank of the holder. Today's Shinto priests hold mokushaku. Geshaku was made of ivory or rhino horn, and mokushaku was made of wood such as Japanese yew and Japanese cherry. According to "Choya gunsai" (Collected Official and Unofficial Writings), the standard size was 36.36 centimeters in length, 8.18 in upper width, 7.27 centimeters in lower width, and 0.90 centimeters in thickness during the mid-Heian period. The shape differed slightly by the holder or purpose of use; there was a set of rules stating that the emperor's shaku usually had a square shape for top and bottom ends, the shaku used during a Shinto ritual had a round shape for top end and a square shape for bottom end, the shaku used by retainers usually had a round shape for top and bottom ends, and the shaku used on celebratory occasions had a square shape for top end and a round shape for bottom end. Furthermore, during some occasions of banquet, shaku was used as impromptu, percussion instruments called shakuhyoshi by the player who held his shaku on the left hand and another person's shaku on the right hand and beating the left shaku with the right shaku to the music; in later years, however, a thicker shaku made especially for the purpose of beating came to be made.
A natural way to read the word 'shaku' is 'kotsu', but since the reading of 'kotsu' also means 'bones' and suggests bad omen, the reading of 'shaku' came to be used. There are other theories to the reason of reading 'shaku'.
Since shaku was formally made of Hahaso oak (Quercus serrata Murray), which is read "saku" in Chinese (pronunciation), the reading developed into "shaku".
The word 'shaku' came from its length which is one shaku (unit of distance approximately equal to 30.3 centimeters).
Shaku and religious services in a shrine
Today, shaku are held by a Shinto priest to give a dignified air to the holder during a ceremony. The formal attire under the dress code of Shinto priests after the Meiji period became the ikan (traditional formal court dress), and it was stipulated that a mokushaku be held as torimono (symbolic offering) at the same time.