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.
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.
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.
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.
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.
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.
Dictsearch - Search a variety of dictionaries including monolingual, bilingual, and specialty dictionaries.
Farlex Free Dictionary - Collection of dictionaries by subject including medical and legal together with free and subscription encyclopedias, in ten languages.
Glossaries - Collection of more than 2400 links to glossaries and dictionaries.
HyperDictionary.com - Includes a thesaurus and searchable dictionaries for English, computers, dreams and medicine.
KnowPlay? - Simple and integrated access to dictionaries, thesauri, encylopedias, and quotation databases.
On-Line Dictionaries - Online specialty dictionaries for English, Russian, German, Finnish and Latin.
The Online Dictionary List - A large directory of online dictionaries, both in English and bilingual, including specialist dictionaries.
Research-It - Includes several dictionaries and a thesaurus as well as online tools for shipping and mailing, currency exchange, and language translation.
Skeptic's Dictionary - Skeptical definitions and essays on occult, paranormal, supernatural and pseudoscientific ideas and practices with references to the best skeptical literature.
Voycabulary - Online dictionary and thesaurus web linking lookup reference tool.
Web Dictionaries - Multi-search tool by Tinh Van, which consults English-only dictionaries, and Vietnamese into English or French translation dictionaries.
Webster's Online Dictionary: The Rosetta Edition - This database doubled with a metasearch tool extracts records from a variety of online and public-domain paper dictionaries, both general and specialized. It offers English definitions, as well as translations from/to a hundred languages.
Word Assault - Looks up multiple words simultaneously using several databases including Webster's, Easton's, Wordnet, and the Devil's Dictionary.
Word Central - Student dictionary and rhyming dictionary online at Merriam-Webster's website. Daily Buzzword by subscription.
Word Spy - Site dedicated to recently coined words and existing words revived into modern usage.
WordWeb - A free English thesaurus and dictionary for Windows.
Worthless Word for the Day - Word-a-day server delivers obscure words not from medical, legal or other professional jargon, with definitions and use citations. Extensive links.