The entries in a Chinese single-character dictionary are arranged according to certain rules and each is provided with pronunciation, definition, and notes on usage. The entries in a Chinese compound-character dictionary are words containing more than one character. These words are arranged simmilar to those in a single-character dictionary and the same type of information is provided. Compound-character dictionaries are generally language dictionaries or phrase dictionaries that include single-character dictionaries but exclude specialized dictionaries and encyclopedias. They focus on words (or idioms, folk sayings, terminology, etc.) but may also provide additional scholarly information.

The Shuowen jiezi (Explaining graphs and analyzing characters), the first extensive single-character Chinese dictionary, was completed in 100 CE, the twelfth regnal year of Yongyuan in the Han dynasty. The author spent the next twenty-two years editing and revising it before submitting the final draft to the emperor in 121 CE, the first regnal year of Jianguang of the Han dynasty. The Erya (The literary expositor) was China’s first compound-character dictionary. It first appeared in the Eastern Zhou dynasty (770–256 BCE), but did not reach its final form (after further editing and expansions) until the Western Han dynasty (206 BCE–24 CE).

The main function of character dictionaries, phrase dictionaries, and encyclopedias (whether monolingual, bilingual, or polyglot) is to serve as a repository of knowledge and as a reference tool. Single-character dictionaries, compound-character dictionaries, and phrase dictionaries all belong to one category of reference books called lexicons and all have specific rules regarding the collection of entries (characters, words, phrases, etc.). Their structures and methods of compilation are similar. The Chinese terms “compound-character dictionary” and “phrase dictionary” can sometimes be used interchangeably.

If you own a compound-character dictionary, do you still need a single-character dictionary? Each has different functions and neither can contain everything you might need to know. One single dictionary cannot possibly be all-encompassing and answer every question. A good dictionary should be well-organized and well-stocked with phrases. It should provide accurate pronunciations, precise definitions, and practical examples. The entries should be easy to search with detailed and reliable indices.

Criteria for the selection of dictionary entries should emphasize accuracy and consistency. Accuracy means that there are no irregular or erroneous entries while consistency means the selection is based on a unified standard and not haphazard.

In addition to being a language source for looking up phrases and characters, a dictionary must first be an orderly repository of collected knowledge (the itemized format allows for the presentation of basic, stable, and important knowledge); second, it must facilitate the spread of knowledge, because a dictionary, acting as a “silent teacher,” can be perused like a regular textbook;  third, it resolves arguments and provides answers to questions people may have in the course of study and work, such as pronunciations, definitions, and usage of characters, phrases, and idioms; and fourth, for research and reference.