Dictionary.com is a free online dictionary service that performs searches across multiple dictionaries, including Dictionary.com Unabridged v. 1.1 (based on the Random House Unabridged Dictionary); The American Heritage® Dictionary of the English Language, Fourth Edition; The American Heritage® Dictionary of Idioms; The American Heritage® Stedman's Medical Dictionary; Merriam-Webster's Dictionary of Law; Merriam-Webster's Medical Dictionary; and Webster's Revised Unabridged Dictionary.
Features:
• Definitions from different dictionaries displayed on a single page for easy cross-reference
• Audio pronunciations and IPA pronunciation keys provided
• Useful extras: Word of the Day, Spanish Word of the Day, Word Explorer (audio podcasts on word origins and usage), language resources (including American Heritage® illustrations, word FAQs, style guide, and reverse dictionary), vocabulary games (including crossword puzzles, word search puzzles, cryptograms, hangman games, and mazes)
• Links to Thesaurus.com, which provides synonyms and antonyms, and Reference.com, which is encyclopedias, almanac, and Web directory combined
Site URL: http://dictionary.reference.com/