Dictionary
A dictionary is a list of words with their definitions, a list of characters with their glyphs, or a list of words with corresponding words in other languages. In a few languages, words can appear in many different forms, but only the lemma form appears as the main word or headword in most dictionaries. Many dictionaries also provide pronunciation information; grammatical information; word derivations, histories, or etymologies; illustrations; usage guidance; and examples in phrases or sentences. Dictionaries are most commonly found in the form of a book. Some dictionaries are also found in electronic portable handheld devices. Dictionaries are produced by lexicographers.

Word order
Today, dictionaries of most languages with alphabetic and syllabic writing systems list words in lexicographic order, usually alphabetical or some analogous phonetic system.

In many languages, words are grouped together according to their true or normal origin ("root"), and these roots are arranged alphabetically. If English dictionaries were arranged like this, the words "import", "export", "support", "report", "porter", "port", "important" and "transportation" would all be listed under "port". This method has the advantage that all words of a common origin are listed together, but the disadvantage is that you have to know how to disassemble all prefixes of a word before you look it up. Some Sanskrit dictionaries and all Arabic dictionaries work like this.

Dictionaries of languages using ideographic writing systems, such as Chinese and Japanese, may be sorted either according to one of many schemes based on the component parts of the characters (number of strokes, overall shape, or pronunciation of each letter), or according to the pronunciation of the full words when spelled phonetically. Due to the unfamiliarity of Chinese speakers with phonetic spellings, phonetic sorts are particularly unsuitable for Chinese dictionaries, while the fluency of Japanese speakers with kana makes kana spelling the most common and convenient method to sort Japanese dictionaries. (See collation for more information on linguistic sorting).

The first English alphabetical dictionary came out in 1604 and alphabetical ordering was a rarity until the 18th century. Before alphabetical listings, dictionaries were organized by topic, i.e. a list of animals all together in one topic.

Prescription and description
Dictionary makers apply two basic philosophies to the defining of words: prescriptive or descriptive. The Oxford English Dictionary (OED) is descriptive, and attempts to describe the actual use of words. Noah Webster, on the other hand, intent on forging a distinct identity for the American language, altered spellings and accentuated differences in meaning and pronunciation of numerous words. This is why American English now uses the spelling "color" while the rest of the world uses "colour". (See American and British English differences.) While disapproved of in the UK, the US spellings are universally understood; likewise the British spellings are not acceptable in America.

While descriptivists argue that prescriptivism is an unnatural attempt to dictate usage or curtail change, prescriptivists argue that to indiscriminately document "improper" or "inferior" usages sanctions those usages by default and causes language to "deteriorate". Although the debate can become very heated, only a small number of controversial words are usually affected. But the softening of usage notations, from the previous edition, for two words, ain't and regardless, out of over 450,000 in Webster's Third in 1961, was enough to provoke outrage among many with prescriptivist leanings, who branded the dictionary as "permissive."

The prescriptive/descriptive issue has been given so much consideration in modern times that most dictionaries of English apply the descriptive method to definitions, while additionally informing readers of attitudes which may influence their choices on words often considered vulgar, offensive, erroneous, or easily confused. Merriam-Webster is subtle, only adding italicized notations such as, sometimes offensive or nonstand (nonstandard.) American Heritage goes further, discussing issues separately in numerous "usage notes." Encarta provides similar notes, but is more prescriptive, offering warnings and admonitions against the use of certain words considered by many to be offensive or illiterate, such as, "an offensive term for..." or "a taboo term meaning..."

Because of the broad use of dictionaries, and their acceptance by many as language authorities, their treatment of the language does affect usage to some degree, even the most descriptive dictionaries providing conservative continuity. In the long run, however, usage primarily determines the meanings of words in English, and the language is being changed and created every day. As Jorge Luis Borges says in the prologue to "El otro, el mismo": "It is often forgotten that (dictionaries) are artificial repositories, put together well after the languages they define. The roots of language are irrational and of a magical nature."

Other variations
Since words and their meanings develop over time, dictionary entries are organized to reflect these changes. Dictionaries may either list meanings in the historical order in which they appeared, or may list meanings in order of popularity and most common use.

Dictionaries also differ in the degree to which they are encyclopedic, providing considerable background information, illustrations, and the like, or linguistic, concentrating on etymology, nuances of meaning, and quotations demonstrating usage.

Any dictionary has been designed to fulfil one or more functions. The dictionary functions chosen by the maker(s) of the dictionary provide the basis for all lexicographic decisions, from the selection of entry words, over the choice of information types, to the choice of place for the information (e.g. in an article or in an appendix). There are two main types of function. The communication-oriented functions comprise text reception (understanding), text production, text revision, and translation. The knowledge-oriented functions deal with situations where the dictionary is used for acquiring specific knowledge about a particular matter, and for acquiring general knowledge about something. The optimal dictionary is one that contains information directly relevant for the needs of the users relating to one or more of these functions. It is important that the information is presented in a way that keeps the lexicographic information costs at a minimum.

History
The art and craft of writing dictionaries is called lexicography.

One of the earliest dictionaries known, and which is still extant today in an abridged form, was written in Latin during the reign of the emperor Augustus. It is known by the title De Significatu Verborum ("On the meaning of words") and was originally compiled by Verrius Flaccus. It was twice abridged in succeeding centuries, first by Sextus Pompeius Festus, and then by Paul the Deacon. Verrius Flaccus' dictionary was an abridged list of difficult or antiquated words, whose usage was illustrated by quotations from early Roman authors.

The Erya, from the early 3rd century BC, was the first Chinese language dictionary. The book organized Chinese characters by semantic groups. The intention of this dictionary was to explain the true meaning and interpretation of words in the context of older ancient texts.

The word "dictionary" comes from neoclassical Latin, diccio, meaning simply "word".

The first true English dictionary was Robert Cawdrey's Table Alphabeticall of 1604, although it only included 3,000 words and the definitions it contained were little more than synonyms. The first one to be at all comprehensive was Thomas Blount's dictionary Glossographia of 1656. This was followed by Samuel Johnson's famous and more complete dictionary of 1755.

In 1806, Noah Webster's dictionary was published by the G&C Merriam Company of Springfield, Massachusetts which still publishes Merriam-Webster dictionaries, but the term Webster's is considered generic and can be used by any dictionary.

The most complete dictionary of the English language is the Oxford English Dictionary. The first edition was properly begun in 1860 and was completed in 1928, by which time a supplement that took an additional five years to complete was already necessary.

Also see A Brief History of English Lexicography