WordNet - WordNet® is a large lexical database of English.
Urban Dictionary - Urban Dictionary is a Web-based dictionary of slang words and phrases.
Artha - Artha is a handy thesaurus based on WordNet with distinct features like global hotkey look-up...
Hinglish Dictionary - HinglishDictionary.com is an archive of user submitted Hinglish words. Users can register and create accounts and add new words, that must have a touch of Hinglish language in it.
Power Thesaurus - Power Thesaurus is a fast, comprehensive and easy-to-follow online thesaurus for writers...
Wiktionary - Open Source wiki-dictionary by the Wikimedia foundation