Urban Dictionary - Urban Dictionary is a Web-based dictionary of slang words and phrases.
Writefull Thesaurus - A Google Docs add-on that uses AI to give you synonyms
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.
Silicon Valley Dictionary - Urban dictionary meets Silicon Valley
Wiktionary - Open Source wiki-dictionary by the Wikimedia foundation
Reverse Dictionary - Describe a concept and get back a list of words