English

The American Heritage Dictionary of the English Language
Online publication of the 4th edition. Featuring audio word pronunciations, illustrations.
http://www.bartleby.com/61/

AskOxford.com
For questions on English grammar, spelling, and usage; to search a dictionary of words, names or quotations; for help with writing; for crosswords and puzzles.
http://www.askoxford.com/

The Beet Foundation
General purpose online English language dictionary and Thesaurus.
http://beetfoundation.com/words/

Collins Word Exchange
Dictionary searches a variety of word and phrase resources, including the Collins English Dictionary, texting abbreviations, internet links, and words submitted by users.
http://www.collins.co.uk/wordexchange/

A Concise Dictionary of Middle English
From A.D. 1150 to 1580. By A.L. Mayhew and Walter W. Skeat. In plain text, or as a zip file, from Project Gutenberg.
http://www.gutenberg.org/etext/10625

DataSegment.com: Online Dictionary
Find definitions by alphabetical browsing or word lookup. Powered by several print dictionaries.
http://onlinedictionary.datasegment.com/

Dictionary of Indian English
Regionalisms defined.
http://www.vsubhash.com/desienglish.asp

Dictionary.net
A dictionary database of word and phrase definitions from eight different sources.
http://www.dictionary.net/

Die.net Online Dictionary
Cross-referenced definitions, spelling correction, and searches from WordNet, Webster's, and a variety of specialized sources. Supports regular expressions and the DICT protocol.
http://dict.die.net/

Elizabethan Dictionary
Provides the origins and meanings of Elizabethan words and vocabulary including obscure Shakespearean expressions.
http://www.william-shakespeare.info/william-shakespeare-dictionary.htm

English-dictionary.us
Fast no-frills English dictionary.
http://www.english-dictionary.us

The English-to-American Dictionary
A humo(u)rous resource for Americans learning British/Scottish English.
http://english2american.com/

Freesearch Dictionary
A British English dictionary powered by the Cambridge University Press that contains around 150,000 words. The site offers a search feature or can be browsed by letter.
http://www.freesearch.co.uk/dictionary

HyperDic
Based on the WordNet lexical database and thesaurus, this dictionary covers only a selection of the most frequent English words. Includes synonyms, antonyms, examples and pronunciation, and links between related words.
http://www.hyperdic.net/

The Jargon Database
A repository of popular neologisms, management speak, and technical terms relevant to various regions, jobs, and cultures, and organized by categories.
http://www.jargondatabase.com

Longman Web Dictionary
Searchable dictionary of contemporary English.
http://www.ldoceonline.com/

Macmillan English Dictionaries
Resource site for the Macmillan range of dictionaries.
http://www.macmillandictionary.com/

New Dictionary Words
An interactive quiz to test you knowledge of new words addd to the Merriam-Webster dictionary.
http://reference.aol.com/quizzes/newwords

Plan of an English Dictionary (1747)
Letter written by Samuel Johnson to the Earl of Chesterfield setting out his plan for an English Dictionary.
http://andromeda.rutgers.edu/~jlynch/Texts/plan.html

SmartDictionary.com
Supports both searching and browsing and encourages user contributions.
http://www.smartdictionary.com/

Suggestive Dictionary
An English dictionary which suggests words as one types. Helps explore new words and meanings.
http://www.objectgraph.com/dictionary/

Ultralingua
Searchable dictionary of the English language, with standard, reverse and phonetic lookup. Also links to a range of other language resources.
http://ultralingua.com/online-dictionary/

Vdictionary.com
Searchable English language dictionary shows results in synonym sets.
http://www.vdictionary.com/

Webster's Unabridged Dictionary of 1913
Forms version. Allows browsing headwords.
http://www.bibliomania.com/2/3/257/

Wiktionary
English language Wiki dictionary from the Wikimedia Foundation.
http://en.wiktionary.org/

Word Sytes
Use this online dictionary to search for definitions in WordNet, Webster's and many other databases.
http://word.sytes.org/

WordIQ Dictionary
Searchable definitions available in a variety of dictionaries including Webster's, a legal dictionary, a dream dictionary, and an encyclopedia.
http://www.wordiq.com/dictionary.html

The Wordsworth Compendium
Program containing over 516,000 English words and phrases to solve word puzzles. Useful for the search and manipulation of words in all aspects of logological activities.
http://dictionary-thesaurus.com/