Dictionaries

General Collections

• Encyberpedia: Dictionaries, Glossaries and Thesauri
• HyperDictionary
  Includes English dictionary, computer dictionary, thesaurus, dream dictionary, and medical dictionary.
• Internet Public Library: Dictionaries
• Know Play? Reference Search
  Multiple dictionary search system.
• OneLook Dictionaries
  A fast dictionary search tool which allows you to look up a word in 37 different dictionaries simultaneously, or pick specific dictionaries from a grouping of subject-specific dictionaries. Includes Internet/computer, science, technology, business, sports, religion, acronym, and general dictionaries. You can also browse the dictionaries individually.
• Oxford Reference Online
  Searchable Oxford University Press dictionaries, guides, and companions for various subjects. Access restricted to TWU.
• Research Institute for the Humanities: Dictionaries and Thesauri
• yourDictionary.com

English Language

• American Heritage Dictionary of the English Language
  3rd ed. via Bartleby.
• ARTFL Project: 1913 Webster's Revised Unabridged Dictionary
• DICT Development Group: Online Dictionary Database Query
  Currently searches several freely available dictionary databases, with over 300,000 total headwords.
• Dictionary.com English Dictionary
  In addition to common English words, includes computer and Internet terms, chemical elements, Bible names and terminology, U.S. cities and Zip Codes, and information on the countries of the world. Search includes Webster's Revised Unabridged Dictionary, WordNet, The Free On-line Dictionary of Computing, Jargon File, The Elements, Easton's 1897 Bible Dictionary, Hitchcock's Bible Names Dictionary, U.S. Gazetteer, The CIA World Factbook.
• Newbury House Dictionary of American English
  40,000 entries providing simple and clear definitions. Provides a wealth of sample sentences, idioms, and a wide array of cultural facts and figures.
• WWWebster Dictionary
  Online version of Merriam-Webster's Collegiate Dictionary.

Multiple Languages

• AllWords.com
  English, French, German, Dutch, Italian, and Spanish.
• iLoveLanguages
  Comprehensive catalog of language-related Internet resources. The over 1900 links have been hand-reviewed. Formerly "Human Languages Page".
• Internet Dictionary Project
• VoyCabulary
  English Dictionary/Thesaurus, Medical, Acronym, Computer, Spanish, German, French, Japanese, Dutch, Swedish, Portuguese, Russian, Hungarian, Welsh.

French

• Dictionnaires d'autrefois
  French dictionaries of the 16th, 17th, 18th and 19th centuries. Searchable version of the 1606 edition of Jean Nicot's Thresor de la Langue Française, a French language dictionary containing over 18,000 entries. Also includes 1694, 1798 and 1835 editions of the Dictionnaire de L'Academie Francaise. From ARTFL Project.
• French-English dictionary [from ARTFL]

German

• German-English Dictionary
• LEO German-English Dictionary

Japanese

Cliches

Law

• Duhaime's Law Dictionary
• Law.com Dictionary

Library and Information Studies

Morse Code

Names

Phrases and Allusions

Rhetoric/Linguistics

• Glossary of Rhetorical Terms with Examples
• Silva Rhetoricae: The Forest of Rhetoric
  Guide to the terms of classical and renaissance rhetoric. By Dr. Gideon Burton, Brigham Young University.

Rhyme

Scientific/Technical

• BioTech Life Science Dictionary
  It's a free, completely searchable dictionary of over 3700 terms relating to the life sciences and medicine
• Free Online Dictionary of Computing
  FOLDOC is a searchable dictionary of acronyms, jargon, programming languages, tools, architecture, operating systems, networking, theory, conventions, standards, mathematics, telecomms, electronics, institutions, companies, projects, products, history, in fact anything to do with computing.
• Glossary of Cartographic Terms
  A lengthy glossary of cartographic terms for use by cartographers, geologists, geographers or hydrologists. Excerpted from Maps for America, 3rd edition.
• MedTerms Medical Dictionary
• Merriam-Webster Medical Dictionary
  Via InteliHealth.
• NetLingo: The Internet Language Dictionary
  Definitions of words which are emerging as a new vocabulary surrounding the technology and community of the Internet and the World Wide Web.
• Webopedia
  Online dictionary and search engine dedicated to computer technology.
• Whatis.com
  Cross-referenced internet and computer terms.

Sign Language

• Basic Dictionary of American Sign Language Terms
  A partial dictionary giving signing instructions for commonly used American Sign Language terms.
• Handspeak
  A practical sign language dictionary online.