Fanqie

Fanqie (Chinese: 反切; pinyin: fǎnqiè; lit. 'reverse cut') is a method in traditional Chinese lexicography to indicate the pronunciation of a monosyllabic character by using two other characters, one with the same initial consonant as the desired syllable and one with the same rest of the syllable (the final). The method was introduced in the 3rd century AD and is to some extent still used in commentaries on the classics and dictionaries.