, also pronounced "tō-in", are Japanese

Japanese language

is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

 kanji

Kanji

Kanji are the adopted logographic Chinese characters hanzi that are used in the modern Japanese writing system along with hiragana , katakana , Indo Arabic numerals, and the occasional use of the Latin alphabet...

 readings imported from China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 by Zen

Zen

Zen is a school of Mahāyāna Buddhism founded by the Buddhist monk Bodhidharma. The word Zen is from the Japanese pronunciation of the Chinese word Chán , which in turn is derived from the Sanskrit word dhyāna, which can be approximately translated as "meditation" or "meditative state."Zen...

 monks and merchants during and after the Song dynasty

Song Dynasty

The Song Dynasty was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a...

. This period roughly corresponds with the mid-Heian

Heian period

The is the last division of classical Japanese history, running from 794 to 1185. The period is named after the capital city of Heian-kyō, or modern Kyōto. It is the period in Japanese history when Buddhism, Taoism and other Chinese influences were at their height...

 to Edo Period

Edo period

The , or , is a division of Japanese history which was ruled by the shoguns of the Tokugawa family, running from 1603 to 1868. The political entity of this period was the Tokugawa shogunate....

 of Japan. During the Muromachi period

Muromachi period

The is a division of Japanese history running from approximately 1336 to 1573. The period marks the governance of the Muromachi or Ashikaga shogunate, which was officially established in 1338 by the first Muromachi shogun, Ashikaga Takauji, two years after the brief Kemmu restoration of imperial...

, they were referred to as . Together, they are collectively known as .

Scholars divide tō-on into two groups: those that are based on Zen of the Middle Ages, and those based on the Obaku

Obaku (school of Buddhism)

The , is , one of three sects of Zen in Japanese Buddhism.-History:Often termed the third sect of Zen Buddhism in Japan, it was established in 1661 by a small faction of masters from China and their Japanese students at Manpuku-ji in Uji, Japan.Today Manpuku-ji serves as the Ōbaku's head temple,...

 school of Buddhism of the Middle Ages. The latter are the readings sometimes referred to as "sō-on".

Tō-on readings are not systematic, as they were introduced piecemeal from China, often along with very specialized terminology.

Examples of words and characters using tō-on readings include: , , , and .