Rime dictionary

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 aimed to reconcile traditions of north and south China to define correct pronunciations for reading the classics and writing poetry. 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).

These dictionaries also record the pronunciations of characters by the fǎnqiè method, using a pair of characters to indicate the onset and remainder of the syllable respectively. The later rime tables gave a significantly more precise and systematic account of the sounds of these dictionaries by tabulating syllables by their onsets, rhyme groups, tones and other properties. The phonological system inferred from these books, often interpreted using the rime tables, is known as Middle Chinese, and has been the key datum for efforts to recover the sounds of early forms of Chinese. It incorporates most of the distinctions found in modern varieties of Chinese, as well as some that are no longer distinguished. It has also been used together with other evidence in the reconstruction of Old Chinese (1st millennium BC).

...
Wikipedia