Duolingo - Duolingo is a free language learning app for iOS, Windows and Android devices. The app makes learning a new language fun by breaking learning into small lessons where you can earn points and move up through the levels. Read more about Duolingo.
Words For That - the reverse-Urban Dictionary of the internet
Synonymful - Improve your vocabulary and communicate like a pro.
Wordd - Quickly look up vocabulary, abbreviations, acronyms, slang
Fluent - Fluent is a people-based marketing platform that uses real-time, one-to-one interaction to create custom audiences and serve personalized ads that drive performance at scale.
Reverse Dictionary - Describe a concept and get back a list of words