A dictionary is a reference book that focuses on defining words and phrases, including multiple meanings. The most frequently used type is a language dictionary that includes the majority of frequently used words in a language. These books 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 along side 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 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 reference books besides the standard English dictionary. There are those for the different dialects of English, ones for other languages, and bilingual dictionaries that help users translate from one language to another. There are those of living languages and others of languages that are preserved only in fragments of ancient manuscript. Still others address specialized areas of language use, such as idioms or political slang.
Variations on this type of book provide some ingenious new types of reference works. Multi-function reference books may combine the properties of a dictionary and a thesaurus. Books that are organized thematically assist the user when he doesn’t know exactly what word he wants. Misspelling dictionaries have entries for the common misspellings of words so that the user can find words even when he doesn’t know how to spell them correctly.
Other reference books address specialty areas, like those that focus on biography and geography. Lacking the full articles of an encyclopedia, they give users a quick introduction to the subject area.