A rime dictionary, rhyme dictionary, or rime book (simplified Chinese: 韵书; traditional Chinese: 韻書; pinyin: yùnshū) is an ancient type of Chinese dictionary that collates characters by tone and rhyme, instead of by radical. The most important rime dictionary tradition began with the Qieyun (601), which codified correct pronunciations for reading the classics and writing poetry by combining the reading traditions of north and south China. This work became very popular during the Tang dynasty, and went through a series of revisions and expansions, of which the most famous is the Guangyun (1007–1008).