Online dictionaries and thesauri belong in this category.
Regular Websites
A service that helps you learn how to interpret acronyms, abbreviations and even Canadian and US postal codes. In total, the Acronym Finder has more than four million acronyms. You can search by acronym or by the definition (e.g. see words associated with computing). - Acronym Finder
http://www.acronymfinder.com/
Alpha Dictionary is a website that helps you search hundreds of free English dictionaries. The site also has historical dictionaries and resources to help you learn slang. The site also has a language blog where you can learn about interesting developments in the use of language. - Alpha Dictionary
http://www.alphadictionary.com
Provides definitions and terminology for those interested in art terms. Whether you are a teacher, student or art collector, you can find much about art here. ArtLex also welcomes contributions from writers who want to share their art expertise. - Artlex
http://www.artlex.com/
An Internet reference and publishing website providing free access to books, reference materials and fiction. Some of the noteworthy reference items available here include Bartlett's familiar quotations, the Columbia Encyclopedia and dictionaries. - Bartleby
http://www.bartleby.com/
Provides access to a variety of reference tools to help you track down the terms you are interested in. Language researchers can use tools on the website to help them in their projects. The website also has resources for English language teaching. - Cambridge Dictionaries Online
http://dictionary.cambridge.org/
The CL Research is an organization that investigates how dictionaries can be used in natural language processing applications. The website also has a variety of electronic dictionaries that can be used for research purposes. You can also obtain dictionary software like DIMAP from this website. - CL Research
http://www.clres.com
Dictionary of the Scots Language
The Dictionary of the Scots Language (DSL) is a major research resource for those interested in Scottish words. The Dictionary is particularly good at covering words in use from the twelve to the seventeenth centuries. You can access a general history of the Scottish people here. - Dictionary of the Scots Language
http://www.dsl.ac.uk/
Free online English dictionary that features a search function, word of the day, word games and crossword puzzles, as well as vocabulary learning resources for many languages and a translator. - Dictionary.com
http://dictionary.reference.com/
Free Dict is a directory of online dictionaries that help you translate from English to other languages. Whether you want to look up words in Japanese, Latin, Norwegian, French, Hungarian, Russian, Spanish or Swedish, this website is a good start. - Free Dict
http://www.freedict.com
The Hyper Dictionary is a website that helps you find definitions of a variety of words, including computing terms and medical terminology. Webmasters can integrate the site's dictionary search feature into their websites. The site is easy and free to use. - Hyper Dictionary
http://www.hyperdictionary.com
Lexical FreeNet is a vocabulary tool that lets you run spell checks on words, find words that rhyme and find connections between words. The website is structured as a search engine that has many different options that can help you find information on words. The website functions by entering words and then you can show relations between words. - Lexical FreeNet
http://www.lexfn.com
Merriam-Webster provides a free online dictionary, thesaurus, audio pronunciations, word of the day, word games, as well as other English language resources. - Merriam-Webster Online
http://www.merriam-webster.com/
Netlingo is a free Internet dictionary that provides definitions of words and phrases of the Internet era, such as presenteeism, premumble, rightsizing, reefer and programmatics. The website also has definitions of acronyms. The website also offers a word of the day email so you can stay appraised of Internet terms. - Netlingo
http://www.netlingo.com
Dictionary of American English. With over 40,000 entries, and simple, clear definitions, this online tool provides a wealth of sample sentences and idioms. - Newbury House Dictionary
http://nhd.heinle.com/
Dictionary search engine offers definitions and translations from a vast selection of online dictionaries, whether in English or in other foreign languages. Site also offers a browsable dictionary database and a reverse dictionary as well. - OneLook
http://www.onelook.com
The Online Etymology Dictionary helps you understand the history and origins of many different English words. The site will be particularly interesting to those studying English or with an interest in the development of the English language. The Dictionary is currently free but also accepts some sponsorship. - Online Etymology Dictionary
http://www.etymonline.com
One of the world's leading sources for definitions of words in the English language. You can look up words in the Oxford English Dictionary Online if you are a subscriber. You can also sign up to receive a ‘Word of the Day’ email to expand your vocabulary. - Oxford English Dictionary
http://www.oed.com/
This website provides the Polish translation of many common English words. Terms are classified alphabetically, and their translations require the installation of a character set to be viewed properly. You can also find a guide to Polish spelling and pronunciation and other general interest pieces, including a recipe for Polish cheesecake. - Polish Dictionary
http://www.polish-dictionary.com
Offers rhyming dictionaries and thesaurus. Includes general information, spelling checker, word finding tools, quotations, quizzes, famous documents and Shakespearean plays and poems. - RhymeZone
http://www.rhymezone.com
Find translations for words and phrases in English or Spanish. - Spanish English Dictionary
http://www.tomisimo.org
Offers language dictionaries, translators, specialty dictionaries, and search engines with huge matrix of bilingual dictionaries and translators. - Stars 21
http://www.stars21.com/
A searchable dictionary of technology and computer related terms and acronyms. - Technology Dictionary
http://www.techdict.org/
Set this site as your homepage for English, medical, legal, financial and computer dictionaries as well as a thesaurus, acronyms, idioms, an encyclopedia and a literature reference library. - The Free Dictionary
http://www.thefreedictionary.com
The Phrase Finder is a British vocabulary website that helps you find the origins and meanings of more than twelve hundred English sayings, idioms and phrases. The website also has a phrase thesaurus that can help make your writing more creative. You can also discuss idioms and sayings on the website's bulletin board. - The Phrase Finder
http://www.phrases.org.uk/
The internet edition of a newspaper column about words and vocabulary, written by Evan Morris. You can access latest issue of the Word Detective, and browse archives the column. Readers can send their suggestions of words to be considered for future columns. - The Word Detective
http://www.word-detective.com
Provides a great source of information on pop culture and new terms. If you're trying to understand what a slang term means, then this is the website for you. The website has over three million definitions of varying quality. - Urban Dictionary
http://www.urbandictionary.com
Vietnamese, English, French, Chinese online dictionaries. English to Vietnamese and Vietnamese to English machine translation - Vdict.com
http://vdict.com
VoyCabulary is a web service that makes it easier to understand complex websites. By entering a URL into the website, the site is then rendered so that you can click on any term and get an instant definition. You can choose from a variety of reference sources including computer and medical dictionaries. - VoyCabulary
http://www.voycabulary.com
Free online dictionary of words, phrases abbreviations related to computer and Internet technology. Includes easy-to-understand definitions, new terms, pronunciation, technical support, job opportunities and links to various resources on the Web. - Webopedia
http://www.webopedia.com
Who Named It is a biographical dictionary of medical terms, with fifteen thousand eponyms in its database. The website also has books available for purchase on nursing, biology, first aid, surgery, genetics and other fields of medicine. You can also search for medical biographies here. - Who Named It
http://www.whonamedit.com
Contains more than one million English words in its database, in addition to other languages. The website also has a phrasebook to help you learn languages quickly. You can also browse for words using the website's grammatical index. Anybody can participate to add new words and definitions to the website. - Wiktionary
http://www.wiktionary.org
A dictionary that enables the user to lookup multiple words at once and receive a personalized definition list. - Word Assault
http://www.wordassault.com/
Explores the meanings of English words from Latin and Greek sources, organized in thematic word units with cross reference searches. - Word Explorations
http://www.wordexplorations.info/
English vocabulary from Latin and Greek sources with prefixes, roots, and suffixes dictionary searches; to assist online learners of all ages. - Word Focus
http://www.wordfocus.com/
A large assortment of word jumbles to unscramble, in various categories. - Word Jumble
http://www.word-jumble.com/
Children's book site for parents, teachers and writers provides book reviews, ideas for reluctant readers, reviews of big books and information on writing for children. - Word Pool
http://www.wordpool.co.uk/
A free online dictionary of English words from Latin and Greek word origins available for learning English words and etymologies with vocabulary definitions. - Word Quests
http://www.wordquests.info/
The Word Smith website is a great resource to learn more about the English language. Two of the website's features are particularly fun: the Anagram Server (fresh anagrams on demand) and the A Word A Day (which helps you learn new and interesting words). You can also use the Wordsmith Chat feature to chat with thinkers, lexicographers and authors. - Word Smith
http://www.wordsmith.org
English vocabulary words from Latin and Greek word origins produced by prefixes, roots, and suffixes as seen in English words. - Word Sources
http://www.wordsources.info/
Word Wizard helps you learn about the origins of English words and phrases and thus improves your vocabulary. If you have a word origin question, you can submit it here to get an answer. It also has some tips on grammar. - Word Wizard
http://www.wordwizard.com/
Offers kids a student dictionary, daily buzzword, and interactive word games. Includes homework help and lesson plans for parents, teachers. By Merriam Webster. - WordCentral.Com
http://www.wordcentral.com/
Your Dictionary is a free dictionary where you can look up words to see what they mean. The site also has glossaries and thesauri to help you find the right word for the right situation. You can also sign up for a word of the day email to expand your vocabulary. - Your Dictionary
http://www.yourdictionary.com/