A dictionary is a list of words with their definitions, a list of characters with its glyph or a list of words with corresponding words in other languages. Many dictionaries also provide pronunciation information, word derivations, histories, or etymologies, illustrations, usage guidance, and examples in sentences.
Dictionaries of alphabetic languages list words in alphabetical order. With non-alphabetic languages, it may be different. The order in a dictionary with ideographic entries such as Chinese character is often troublesome and controversial because each character has different readings. Collation systems for logographs do exist. In Japanese and Korean, words containing Chinese characters (called Kanji in Japanese and Hanja in Korean) can be spelled in Hiragana and Hangul respectively, and so are inserted in their proper alphabetical order in dictionaries, alongside words not derived from Chinese characters. Furthermore, in entries for words derived from characters, the main entry words are spelled in Hiragana (for Japanese dictionaries) and Hangul (for Korean dictionaries), with the Chinese characters inserted in parentheses after each entry word.
Another variant is the glossary, an alphabetical list of defined terms in a specialized field, such as medicine or science. The simplest dictionary, a defining dictionary, provides a core glossary of the simplest meanings of the simplest concepts. From these, other concepts can be explained and defined, in particular for those who are first learning a language. In English the commercial defining dictionaries typically include only one or two meanings of under 2000 words. With these, the rest of English, and even the 4000 most common English idioms and metaphors, can be defined.
Most modern dictionaries are descriptive, although many, such as the American Heritage dictionaries make extensive efforts to provide information on the best usage, and almost all dictionaries provide some information on words considered erroneous, vulgar, or easily confused. In any case, in the long run, usage alone determines the meaning of words, although dictionaries provide conservative continuity, even the most descriptive.
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.
Picture Dictionary Online Picture Dictionary with search function. Uses pictures and symbols from Universal Picture Language. Grasp the meaning of a word with just a glance at its representative picture.
Open Dictionary Offers various definitions, translations and pronunciations in many languages (uses Wiktionary and WordNet for most of its entries).
An open content dictionary project is the GNU Collaborative International Dictionary of English (GCIDE). This dictionary uses Webster's Revised Unabridged Dictionary (1913) and WordNet as its sources and is being developed collaboratively under the terms of the GNU General Public License. It describes itself as "a freely-available set of ASCII files containing the marked-up text of a substantial English dictionary".
OneLook Dictionaries Look up a word or term in an Internet dictionary or glossary. Free search access to a frequently updated database of words, terms, names, and acronyms. http://www.onelook.com/
Merriam-Webster OnLine A free, searchable on-line dictionary and thesaurus, word games, a word of the day, and many other English language and vocabulary reference tools and resources. http://www.m-w.com/
The Online Dictionary List A large directory of online dictionaries, both in English and bilingual, including specialist dictionaries. http://www.clearenglish.net/dictionary.htm
Dictionary Link A directory of free online language resources such as dictionaries, thesauruses, language translators, and encyclopedias. http://www.dictionarylink.com/
1000Dictionaries.com Links to online language dictionaries and subject dictionaries. http://www.1000dictionaries.com/
Cooldictionary.com Free edition of a complete Webster dictionary. Fully crosslinked. http://www.cooldictionary.com/
Skeptic's Dictionary Skeptical definitions and essays on occult, paranormal, supernatural and pseudoscientific ideas and practices with references to the best skeptical literature. http://skepdic.com/
Information Please Dictionary Infoplease's free online dictionary. Features almanacs, an encyclopedia, and an atlas. http://www.infoplease.com/dictionary.html
Dictionary Society of North America An international organization of librarians, booksellers, translators, linguists, publishers, writers, journalists, and collectors. Founded in 1975 to further research in dictionary making, study, collection, and use. Member of the American Council of Learned Societies. http://polyglot.lss.wisc.edu/dsna/index.html
Quotations: The Yale Dictionary Project to create an searchable online database and a quotation dictionary from Yale University Press. http://quotationdictionary.com/
High Definition Dictionary Mixed collection of drug terminology with an apparently arbitrarily selected mix of other, unrelated terms. Dictionary accepts contributions of new terms. http://hdd.rox.com/
The Century Dictionary Online Free 500,000 word dictionary of English with an encyclopedia and world atlas. Uses DjVu and JPEG formats to display page images. Has headword lookup and full text search of 22 million words of underlying text. http://www.global-language.com/CENTURY/
Lighting Design Terminology Explanations of terms used in architectural lighting and lighting simulation. http://www.schorsch.com/kbase/glossary/
Word Spy Site dedicated to recently coined words and existing words revived into modern usage. http://www.wordspy.com/
DICT Development Group A WWW interface to several freely available on-line dictionaries, including Webster's 1913, the Jargon File, the US Gazetteer, and Easton's Bible Dictionary. http://www.dict.org/
Strange Dictionaries Free online versions of the Dictionary of One-Letter Words, the Dictionary of All-Vowel Words, the Dictionary of All-Consonant Words, and other strange dictionary resources. http://www.blueray.com/dictionary/
The Superhero Dictionary Each entry compares a superhero's name with its real life meaning and includes comparison pictures and pronunciations. http://SHDictionary.tripod.com/
Dictionary of Difficult Words Search or browse this dictionary of more than 13,000 words. http://www.tiscali.co.uk/reference/dictionaries/difficultwords/
AllWords.com Features two modern English dictionaries, multilingual search, and translation. Also features a guide to language sites on the web and a language discussion forum. http://www.allwords.com/
Worthless Word for the Day Obscure, abstruse and/or recondite word, especially one not falling into medical terms, foreign monetary units, foreign units of measure, legal terms, or professional jargon of any type. http://members.aol.com/tsuwm/
A-Z-Dictionaries Descriptions and links to free online dictionaries, the Merriam-Webster dictionary, electronic dictionary products, dictionary downloads and software and ideas for saving money. http://a-z-dictionaries.com/
Dictsearch Search a variety of dictionaries including monolingual, bilingual, and specialty dictionaries. http://www.foreignword.com/Tools/dictsrch.htm
Glossaries Collection of more than 2000 links to glossaries and dictionaries. http://www.jump.net/~fdietz/glossary.htm
The Glossarist Searchable directory of glossaries and topical dictionaries containing terms and definitions on hundreds of subjects. http://www.glossarist.com/
KnowPlay? Simple and integrated access to dictionaries, thesauri, encylopedias, and quotation databases. http://www.kplay.cc/reference.html
Lexicate Online Dictionary Text-only online dictionary directory of language (e.g. English, French and Spanish) and subject (e.g. Science, Computer and Medical) dictionaries. http://www.lexicate.com/
Lexicool Searchable directory of bilingual and multilingual dictionaries. http://www.lexicool.com/
On-Line Dictionaries Online specialty dictionaries for English, Russian, German, Finnish and Latin. http://www.ets.ru/udict-e.htm
Searchbug A collection of reference tools. http://www.searchbug.com/reference/
Voycabulary Online dictionary and thesaurus web linking lookup reference tool. http://www.voycabulary.com/
WordWeb A free English thesaurus and dictionary for Windows. http://www.wordweb.co.uk/free
Xlation.com Glossary Database More than 1682 separate glossaries, linked by topic and by ISO 639-2 language codes. http://www.xlation.com/glossaries/
yourDictionary.com Comprehensive index of on-line dictionaries in more than 200 different languages. Includes an index of on-line grammars, word of the day by email, and several pages of linguistic fun. http://www.yourdictionary.com/