反 切 [a traditional method of indicating the pronunciation of a Chinese character by using two other Chinese characters，the first having the same consonant as the given character and the second having the same vowel (with or without final nasal) and tone] 古汉语注
反切是古人在“直音”、“读若”之后创制的一种注音方法，又称“反”、“切”、“翻”、“反语”等。反切的基本规则是用两个汉字相拼给一个字注音，切上字取声母，切下字取韵母和声调。