Lingo Web Dictionary

With Lingo, you are never stopped by words you don’t know again. While you
are browsing online, you can double-click on words you don’t know. Lingo
will show you the meanings, sounds, and importance of the words. It’s a
quick and easy way to build up your vocabulary and make reading fun!

Built on natural language processing technology, Lingo prompts users to
learn new words and saves those to a word collection to be reviewed down the
road. They can practice their words with automatically generated flashcards
and quizzes.

Try it here.