Kan-on in the context of Japanese phonology

A single kanji might have multiple on'yomi pronunciations, reflecting the Chinese pronunciations from different time periods or regions. On'yomi pronunciations are generally classified into go-on, kan-on, tō-on and kan'yō-on, roughly based on when they were borrowed from Chinese during the peaks of the Sinosphere.

Shingon (真言宗, Shingon-shū; "True Word/Mantra School") is one of the major schools of Buddhism in Japan and one of the few surviving Vajrayana lineages in East Asian Buddhism. It is a form of Japanese Esoteric Buddhism and is sometimes called "Tōmitsu" (東密 lit. "Esoteric [Buddhism] of Tō-ji"). The word shingon is the Japanese reading of the Chinese word 真言 (zhēnyán), which is the translation of the Sanskrit word mantra.

The Zhenyan lineage was founded in China (c. 7th–8th centuries) by Indian vajrācāryas (esoteric masters) like Śubhakarasiṃha, Vajrabodhi and Amoghavajra. These esoteric teachings would later flourish in Japan under the auspices of a Buddhist monk named Kūkai (空海, 774–835), who traveled to Tang China and received these esoteric transmissions from a Chinese master named Huiguo (746–805). Kūkai established his tradition at Mount Kōya (in Wakayama Prefecture), which remains the central pilgrimage center of Shingon Buddhism.

Go-on or goon (呉音; English: /ˈɡoʊ.ɒn/ GOH-on; Japanese pronunciation: [ɡo.oɴ] or [ɡoꜜoɴ], "sounds from the Wu region") are Japanese kanji readings based on the classical pronunciations of Chinese characters of the historically prestigious eastern Jiankang (now Nanjing) dialect.

Go-on are the earliest form of on'yomi (音読み), preceding the kan-on (漢音) readings. Both go-on and kan-on exhibit characteristics of Middle Chinese.