Wiktionary

Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 150 languages. Unlike standard dictionaries, it is written collaboratively by volunteers using wiki software, allowing articles to be changed by almost anyone with access to the Web site.

Like its sister project Wikipedia, Wiktionary is run by the Wikimedia Foundation. Because Wiktionary is not limited by print space considerations, most of Wiktionary's language editions provide definitions and translations of words from many languages, and some editions offer additional information typically found in thesauruses and lexicons. Additionally, the English Wiktionary now includes Wikisaurus, a category that serves as a thesaurus, including lists of slang words. "Wikisaurus"