Wordnik is described as 'online English dictionary and language resource that provides dictionary and thesaurus content.Some of the content is based on print dictionaries such as the Century Dictionary, the American Heritage Dictionary, WordNet, and GCIDE' and is an website in the Education & Reference category. There are more than 25 alternatives to Wordnik, not only websites but also apps for a variety of platforms, including iPhone, Android, Windows and Linux. The best alternative is GoldenDict, which is both free and Open Source. Other great sites and apps similar to Wordnik are Wiktionary (Free, Open Source), Linguee (Free), WordReference (Freemium) and Dictionary.com (Free).
GoldenDict is an open-source dictionary program for PC computers that gives translations of words and phrases for different languages. It allows use of several popular dictionary file formats simultaneously.
Google's dictionary extension on Google Chrome. With it, you can double-click any word to view its definition in a small pop-up bubble, or search the complete definition of any word or phrase using the address bar dictionary.
Lion allows you to send a query to the German-English, -French, -Spanish and -Italian LEO dictionaries (Chinese is currently not supported) with a click of your mouse from almost all MS Windows applications.
Reference.com offers a massive online dictionary, thesaurus, encyclopedia, quote finder, and translator (powered by Google Translate)- all for free. For the Dictionary.com and Thesaurus.com mobile app, go here. Dictionary.com