There are many free on-line dictionaries and encyclopedias that will aid your English studies. Some of the better and easy to use ones include: Wikipedia, Wiktionary, and the Merrium-Webster dictionary and thesaurus.
For slang and new words check out Urban Dictionary:.
The Visual Dictionary provides diagrams and pictures to help you understand the meaning of words.
HighBeam Encyclopedia is a search engine that links you to over a hundred on-line dictionaries and encyclopedias.
The Double-Tongued Dictionary offers the word-nerd a lexicon of fringe English, jargon, and new words.
Be sure to check in regularly as i will be posting other helpful sites from time to time.