A dictionary is a reference book that focuses on defining words and phrases, including multiple meanings. The most frequently used dictionary is a language dictionary that includes the majority of frequently used words in a language. Language dictionaries are made for different types of users: scholars, office workers, schools, and second language learners.

Adult English language dictionaries characteristically include hyphenation information, pronunciation guides, part of speech, alternate spellings, etymological information, sample sentences, usage notes, and sometimes synonyms. Cross-references may be used for less-used forms—such as British variations in a dictionary of American English, and charts and illustrations may help amplify the definitions.

There are many competing dictionaries put out by different companies. Not only do they have different forms — paperback, hardbound, and online editions — but they differ in other ways. Each company, for example, uses its own version of phonetic respelling based on the research done by its experts. One company might use the International Phonetic Alphabet (IPA), while others have proprietary pronunciation symbols, and still others use the letters of the alphabet in a special way to indicate pronunciation.

Other differences between dictionaries show up in other features. Many dictionaries include their experts’ guidance on grammar, usage, and the history of the English language. Definitions differ slightly, and sample sentences may be the work of the editorial staff or taken from real-world usage, perhaps the first known written use, when possible.

There are other types of language dictionaries besides the standard English dictionary. There are dictionaries for the different dialects of English, dictionaries for other languages, and bilingual dictionaries that help you translate from one language to another. There are dictionaries of living languages and dictionaries of languages that are preserved only in fragments of ancient manuscript, and dictionaries that address specialized areas of language use, such as idioms or political slang.

Variations on the dictionary provide some ingenious new types of reference works. Multi-function dictionaries may combine the properties of a dictionary and a thesaurus. Dictionaries organized thematically assist you when you don’t know exactly what word you want. Misspelling dictionaries have entries for the common misspellings of words so that you can find words even when you don’t know how to spell them correctly.

Other dictionaries address specialty areas, like dictionaries of biography and dictionaries of geography. Lacking the full articles of an encyclopedia, they give users a quick introduction to the subject area.